Supporting 4 way connections in LKSCTP

Supporting 4 way connections in LKSCTP

[Sun Paul]

Hi

we have a problem on using LKSCTP to form a 4 ways multi-homing network.

Configuration
- Node-A has 2 IP addresses in different subnets, known as IP-A (eth1),
IP-B (eth2)
- Node-B has 2 IP addresses in different subnets, known as IP-X (eth1),
IP-Y (eth2)

the four way paths are shown below.
1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
4. IP-B (12.1.1.1) to IP-X (11.1.1.11)

the HB/HB_ACK is normal for the paths " IP-A to IP-X" and "IP-B to
IP-Y", but it is not correct for the rest of two.

First of all, we are using iproute2 to form 2 table such that when
IP-B arrives on IP-X, it will know how to route back to IP-B on the
same interface, i.e (eth1). Same logic for the path "IP-A to IP-X".

What we observed here is that when 12.1.1.1 sends INIT to 11.1.1.11,
LKSCTP will send back the INIT_ACK to 12.1.1.1 using 12.1.1.11 but not
using the IP 11.1.1.11.

The above operation makes the subsequence HB/HB_ACK in using wrong IP address.

TCP trace on eth1
18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
[init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]

TCP trace on eth2
18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
[init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
3340756356]
18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]


If we are using single homing, there is no problem on the SCTP
communication. Below is the TCP trace on eth1 using sctp_test

18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
[init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
[init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16] [init TSN:
1877695021]
18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [DATA]
(B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [SACK]
[cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]

>From the observations, it seems that the LKSCTP library is not able to
use the original local address when multi-homing is being used. Is
there anyway can be resolved it?

Thanks

PS

Re: Supporting 4 way connections in LKSCTP

[Vlad Yasevich]

On 11/25/2013 08:03 PM, Sun Paul wrote:
> Hi
> 
> we have a problem on using LKSCTP to form a 4 ways multi-homing network.
> 
> Configuration
> - Node-A has 2 IP addresses in different subnets, known as IP-A (eth1),
> IP-B (eth2)
> - Node-B has 2 IP addresses in different subnets, known as IP-X (eth1),
> IP-Y (eth2)
> 

First of all, this is not a 4 way multi-homed network.  As far as each
SCTP association is concerned, it has only 2 destinations to send to
so it has only 2 ways to get there.  The fact that you have multiple
local addresses doesn't mean that every local address can and should
be used to connect to the remote.

> the four way paths are shown below.
> 1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
> 2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
> 3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
> 4. IP-B (12.1.1.1) to IP-X (11.1.1.11)

No, actually you only have 2 paths:  one to IPX and one to IP-Y.
Which source address you choose is based on routing policy
decisions and is outside the scope of SCTP.

> 
> the HB/HB_ACK is normal for the paths " IP-A to IP-X" and "IP-B to
> IP-Y", but it is not correct for the rest of two.

Right, because linux is using a host addressing model, not an interface
addressing model.  SCTP stack simply finds the best source address
that can be used to reach IP-X and it happens to be IP-A.  So that
is what it is going to use.

The above explains why you are seeing what you describe below.

In the end, linux SCTP implementation determines paths solely based
on the destination address.

-vlad

> 
> First of all, we are using iproute2 to form 2 table such that when
> IP-B arrives on IP-X, it will know how to route back to IP-B on the
> same interface, i.e (eth1). Same logic for the path "IP-A to IP-X".
> 
> What we observed here is that when 12.1.1.1 sends INIT to 11.1.1.11,
> LKSCTP will send back the INIT_ACK to 12.1.1.1 using 12.1.1.11 but not
> using the IP 11.1.1.11.
> 
> The above operation makes the subsequence HB/HB_ACK in using wrong IP address.
> 
> TCP trace on eth1
> 18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
> [init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
> 18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
> 18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
> 18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
> 18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
> 18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
> 18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
> 
> TCP trace on eth2
> 18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
> [init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
> 3340756356]
> 18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
> 18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
> 18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
> 18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
> 18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
> 18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
> 18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
> 18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
> 18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
> 
> 
> If we are using single homing, there is no problem on the SCTP
> communication. Below is the TCP trace on eth1 using sctp_test
> 
> 18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
> [init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
> 18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
> [init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16] [init TSN:
> 1877695021]
> 18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
> 18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
> 18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
> 18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
> 18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [DATA]
> (B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
> 18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [SACK]
> [cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
> 18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
> 18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
> 
> From the observations, it seems that the LKSCTP library is not able to
> use the original local address when multi-homing is being used. Is
> there anyway can be resolved it?
> 
> Thanks
> 
> PS
> --
> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

Re: Supporting 4 way connections in LKSCTP

[Sun Paul]

Hi Vlad

Thank for your reply. If it is based on the destination IP to find the
best route, why the problem didn't happen on single-homing sample?

In the single-homing sample that provided in the original email, both
of the interfaces (eth1 and eth2) are presented on NODE-B during the
test. However, the LKSCTP library know to use the interface eth1 to
respond to the SCTP request.

- PS

On Wed, Nov 27, 2013 at 7:09 AM, Sun Paul <paulrbk@gmail.com> wrote:
> Hi Vlad
>
> Thank for your reply. If it is based on the destination IP to find the
> best route, why the problem didn't happen on single-homing sample?
>
> In the single-homing sample that provided in the original email, both
> of the interfaces (eth1 and eth2) are presented on NODE-B during the
> test. However, the LKSCTP library know to use the interface eth1 to
> respond to the SCTP request.
>
> - PS
>
> On Tue, Nov 26, 2013 at 11:19 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>> On 11/25/2013 08:03 PM, Sun Paul wrote:
>>> Hi
>>>
>>> we have a problem on using LKSCTP to form a 4 ways multi-homing network.
>>>
>>> Configuration
>>> - Node-A has 2 IP addresses in different subnets, known as IP-A (eth1),
>>> IP-B (eth2)
>>> - Node-B has 2 IP addresses in different subnets, known as IP-X (eth1),
>>> IP-Y (eth2)
>>>
>>
>> First of all, this is not a 4 way multi-homed network.  As far as each
>> SCTP association is concerned, it has only 2 destinations to send to
>> so it has only 2 ways to get there.  The fact that you have multiple
>> local addresses doesn't mean that every local address can and should
>> be used to connect to the remote.
>>
>>> the four way paths are shown below.
>>> 1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
>>> 2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
>>> 3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
>>> 4. IP-B (12.1.1.1) to IP-X (11.1.1.11)
>>
>> No, actually you only have 2 paths:  one to IPX and one to IP-Y.
>> Which source address you choose is based on routing policy
>> decisions and is outside the scope of SCTP.
>>
>>>
>>> the HB/HB_ACK is normal for the paths " IP-A to IP-X" and "IP-B to
>>> IP-Y", but it is not correct for the rest of two.
>>
>> Right, because linux is using a host addressing model, not an interface
>> addressing model.  SCTP stack simply finds the best source address
>> that can be used to reach IP-X and it happens to be IP-A.  So that
>> is what it is going to use.
>>
>> The above explains why you are seeing what you describe below.
>>
>> In the end, linux SCTP implementation determines paths solely based
>> on the destination address.
>>
>> -vlad
>>
>>>
>>> First of all, we are using iproute2 to form 2 table such that when
>>> IP-B arrives on IP-X, it will know how to route back to IP-B on the
>>> same interface, i.e (eth1). Same logic for the path "IP-A to IP-X".
>>>
>>> What we observed here is that when 12.1.1.1 sends INIT to 11.1.1.11,
>>> LKSCTP will send back the INIT_ACK to 12.1.1.1 using 12.1.1.11 but not
>>> using the IP 11.1.1.11.
>>>
>>> The above operation makes the subsequence HB/HB_ACK in using wrong IP address.
>>>
>>> TCP trace on eth1
>>> 18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>> [init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>> 18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>> 18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>> 18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>> 18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>> 18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>> 18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>
>>> TCP trace on eth2
>>> 18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>> [init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>> 3340756356]
>>> 18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>> 18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>> 18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>> 18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>> 18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>> 18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>> 18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>> 18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>> 18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>
>>>
>>> If we are using single homing, there is no problem on the SCTP
>>> communication. Below is the TCP trace on eth1 using sctp_test
>>>
>>> 18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>> [init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>> 18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>> [init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16] [init TSN:
>>> 1877695021]
>>> 18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>> 18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>> 18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>> 18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>> 18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [DATA]
>>> (B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
>>> 18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [SACK]
>>> [cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
>>> 18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>> 18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>
>>> From the observations, it seems that the LKSCTP library is not able to
>>> use the original local address when multi-homing is being used. Is
>>> there anyway can be resolved it?
>>>
>>> Thanks
>>>
>>> PS
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>
>>

Re: Supporting 4 way connections in LKSCTP

[Neil Horman]

On Wed, Nov 27, 2013 at 07:10:49AM +0800, Sun Paul wrote:
> Hi Vlad
> 
> Thank for your reply. If it is based on the destination IP to find the
> best route, why the problem didn't happen on single-homing sample?
> 
Because You only ever use one address from NODE A (12.1.1.1)

> In the single-homing sample that provided in the original email, both
> of the interfaces (eth1 and eth2) are presented on NODE-B during the
> test. However, the LKSCTP library know to use the interface eth1 to
> respond to the SCTP request.
> 
Yes, because it does a route lookup to each of the two ip addresses to NODE B,
and in both lookups, the route indicates that only one source address should be
used (12.1.1.1).  If you issue a ip route show command, you'll see that routes
to both address on NODE B match on a rule that specifies the same src address
and interface be used.

Neil

> - PS
> 
> On Wed, Nov 27, 2013 at 7:09 AM, Sun Paul <paulrbk@gmail.com> wrote:
> > Hi Vlad
> >
> > Thank for your reply. If it is based on the destination IP to find the
> > best route, why the problem didn't happen on single-homing sample?
> >
> > In the single-homing sample that provided in the original email, both
> > of the interfaces (eth1 and eth2) are presented on NODE-B during the
> > test. However, the LKSCTP library know to use the interface eth1 to
> > respond to the SCTP request.
> >
> > - PS
> >
> > On Tue, Nov 26, 2013 at 11:19 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
> >> On 11/25/2013 08:03 PM, Sun Paul wrote:
> >>> Hi
> >>>
> >>> we have a problem on using LKSCTP to form a 4 ways multi-homing network.
> >>>
> >>> Configuration
> >>> - Node-A has 2 IP addresses in different subnets, known as IP-A (eth1),
> >>> IP-B (eth2)
> >>> - Node-B has 2 IP addresses in different subnets, known as IP-X (eth1),
> >>> IP-Y (eth2)
> >>>
> >>
> >> First of all, this is not a 4 way multi-homed network.  As far as each
> >> SCTP association is concerned, it has only 2 destinations to send to
> >> so it has only 2 ways to get there.  The fact that you have multiple
> >> local addresses doesn't mean that every local address can and should
> >> be used to connect to the remote.
> >>
> >>> the four way paths are shown below.
> >>> 1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
> >>> 2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
> >>> 3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
> >>> 4. IP-B (12.1.1.1) to IP-X (11.1.1.11)
> >>
> >> No, actually you only have 2 paths:  one to IPX and one to IP-Y.
> >> Which source address you choose is based on routing policy
> >> decisions and is outside the scope of SCTP.
> >>
> >>>
> >>> the HB/HB_ACK is normal for the paths " IP-A to IP-X" and "IP-B to
> >>> IP-Y", but it is not correct for the rest of two.
> >>
> >> Right, because linux is using a host addressing model, not an interface
> >> addressing model.  SCTP stack simply finds the best source address
> >> that can be used to reach IP-X and it happens to be IP-A.  So that
> >> is what it is going to use.
> >>
> >> The above explains why you are seeing what you describe below.
> >>
> >> In the end, linux SCTP implementation determines paths solely based
> >> on the destination address.
> >>
> >> -vlad
> >>
> >>>
> >>> First of all, we are using iproute2 to form 2 table such that when
> >>> IP-B arrives on IP-X, it will know how to route back to IP-B on the
> >>> same interface, i.e (eth1). Same logic for the path "IP-A to IP-X".
> >>>
> >>> What we observed here is that when 12.1.1.1 sends INIT to 11.1.1.11,
> >>> LKSCTP will send back the INIT_ACK to 12.1.1.1 using 12.1.1.11 but not
> >>> using the IP 11.1.1.11.
> >>>
> >>> The above operation makes the subsequence HB/HB_ACK in using wrong IP address.
> >>>
> >>> TCP trace on eth1
> >>> 18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
> >>> [init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
> >>> 18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
> >>> 18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
> >>> 18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
> >>> 18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
> >>> 18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
> >>> 18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
> >>>
> >>> TCP trace on eth2
> >>> 18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
> >>> [init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
> >>> 3340756356]
> >>> 18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
> >>> 18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
> >>> 18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
> >>> 18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
> >>> 18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
> >>> 18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
> >>> 18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
> >>> 18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
> >>> 18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
> >>>
> >>>
> >>> If we are using single homing, there is no problem on the SCTP
> >>> communication. Below is the TCP trace on eth1 using sctp_test
> >>>
> >>> 18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
> >>> [init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
> >>> 18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
> >>> [init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16] [init TSN:
> >>> 1877695021]
> >>> 18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
> >>> 18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
> >>> 18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
> >>> 18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
> >>> 18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [DATA]
> >>> (B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
> >>> 18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [SACK]
> >>> [cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
> >>> 18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
> >>> 18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
> >>>
> >>> From the observations, it seems that the LKSCTP library is not able to
> >>> use the original local address when multi-homing is being used. Is
> >>> there anyway can be resolved it?
> >>>
> >>> Thanks
> >>>
> >>> PS
> >>> --
> >>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
> >>> the body of a message to majordomo@vger.kernel.org
> >>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >>>
> >>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

Re: Supporting 4 way connections in LKSCTP

[Sun Paul]

How LKSCTP select which source address to use for the INIT_ACK or
HB_ACK? below is the testing result where a router is located in the
middle.

Before starting the application. the packet on eth1 and eth2 are

eth1
0 packets dropped by kernel
[root@localhost ~]# tcpdump -i eth1 -s 0 -nn
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
11:24:14.262489 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
[init tag: 28362903] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
11:24:14.262522 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
11:24:14.539486
11:24:16.262488 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
[init tag: 29391734] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
11:24:16.262520 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]

eth2
[root@localhost ~]# tcpdump -i eth2 -s 0 -nn
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes

When starting the application. the packet show as below.

eth1
11:26:02.261511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
[init tag: 26256828] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
11:26:02.263513 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [COOKIE ECHO]
11:26:02.264518 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
11:26:02.563511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]

eth2
11:26:02.261604 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
[init tag: 3478239387] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
2330749678]
11:26:02.263583 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
11:26:02.264548 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
11:26:02.264652 IP 11.1.1.1.2905 > 120.1.1.1.2905: sctp (1) [HB REQ]
11:26:02.264705 IP 120.1.1.1.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
11:26:02.563543 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]

>From the above result, you can see that the INIT, COOKIE ECHO and
HB_REQ originated from 12.1.1.1 on eth1, but the ACK (INIT_ACK,
COOKIE_ACK, HB_ACK) are returned on eth2 using source address
120.1.1.1 instead of 110.1.1.1.

Why LKSCTP use 120.1.1.1 as source instead of 110.1.1.1?

For simple ICMP ping test, it is normal, but not for SCTP.

eth1
11:30:02.824548 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
seq 12, length 64
11:30:02.824559 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
seq 12, length 64
11:30:03.825551 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
seq 13, length 64
11:30:03.825561 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
seq 13, length 64

eth2
11:30:34.027687 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
seq 2, length 64
11:30:34.027697 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
seq 2, length 64
11:30:35.027686 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
seq 3, length 64
11:30:35.027694 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
seq 3, length 64

Below is the route information
#route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
110.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth1
120.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth2

# ip route show
110.1.1.0/24 dev eth1  proto kernel  scope link  src 110.1.1.1
120.1.1.0/24 dev eth2  proto kernel  scope link  src 120.1.1.1

Since we are using iproute2, so we will have dedicate routing table
per interface

# ip route show table SCTP1
default via 110.1.1.254 dev eth1

# ip route show table SCTP2
default via 120.1.1.254 dev eth2

# ip rule ls
0: from all lookup local
101: from 110.1.1.1 lookup SCTP1
102: from 120.1.1.1 lookup SCTP2
32766: from all lookup main
32767: from all lookup default

How LKSCTP select source address to reply? If we know how it works,
then we may know what is going wrong.

On Wed, Nov 27, 2013 at 8:45 PM, Neil Horman <nhorman@tuxdriver.com> wrote:
> On Wed, Nov 27, 2013 at 07:10:49AM +0800, Sun Paul wrote:
>> Hi Vlad
>>
>> Thank for your reply. If it is based on the destination IP to find the
>> best route, why the problem didn't happen on single-homing sample?
>>
> Because You only ever use one address from NODE A (12.1.1.1)
>
>> In the single-homing sample that provided in the original email, both
>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>> test. However, the LKSCTP library know to use the interface eth1 to
>> respond to the SCTP request.
>>
> Yes, because it does a route lookup to each of the two ip addresses to NODE B,
> and in both lookups, the route indicates that only one source address should be
> used (12.1.1.1).  If you issue a ip route show command, you'll see that routes
> to both address on NODE B match on a rule that specifies the same src address
> and interface be used.
>
> Neil
>
>> - PS
>>
>> On Wed, Nov 27, 2013 at 7:09 AM, Sun Paul <paulrbk@gmail.com> wrote:
>> > Hi Vlad
>> >
>> > Thank for your reply. If it is based on the destination IP to find the
>> > best route, why the problem didn't happen on single-homing sample?
>> >
>> > In the single-homing sample that provided in the original email, both
>> > of the interfaces (eth1 and eth2) are presented on NODE-B during the
>> > test. However, the LKSCTP library know to use the interface eth1 to
>> > respond to the SCTP request.
>> >
>> > - PS
>> >
>> > On Tue, Nov 26, 2013 at 11:19 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>> >> On 11/25/2013 08:03 PM, Sun Paul wrote:
>> >>> Hi
>> >>>
>> >>> we have a problem on using LKSCTP to form a 4 ways multi-homing network.
>> >>>
>> >>> Configuration
>> >>> - Node-A has 2 IP addresses in different subnets, known as IP-A (eth1),
>> >>> IP-B (eth2)
>> >>> - Node-B has 2 IP addresses in different subnets, known as IP-X (eth1),
>> >>> IP-Y (eth2)
>> >>>
>> >>
>> >> First of all, this is not a 4 way multi-homed network.  As far as each
>> >> SCTP association is concerned, it has only 2 destinations to send to
>> >> so it has only 2 ways to get there.  The fact that you have multiple
>> >> local addresses doesn't mean that every local address can and should
>> >> be used to connect to the remote.
>> >>
>> >>> the four way paths are shown below.
>> >>> 1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
>> >>> 2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
>> >>> 3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
>> >>> 4. IP-B (12.1.1.1) to IP-X (11.1.1.11)
>> >>
>> >> No, actually you only have 2 paths:  one to IPX and one to IP-Y.
>> >> Which source address you choose is based on routing policy
>> >> decisions and is outside the scope of SCTP.
>> >>
>> >>>
>> >>> the HB/HB_ACK is normal for the paths " IP-A to IP-X" and "IP-B to
>> >>> IP-Y", but it is not correct for the rest of two.
>> >>
>> >> Right, because linux is using a host addressing model, not an interface
>> >> addressing model.  SCTP stack simply finds the best source address
>> >> that can be used to reach IP-X and it happens to be IP-A.  So that
>> >> is what it is going to use.
>> >>
>> >> The above explains why you are seeing what you describe below.
>> >>
>> >> In the end, linux SCTP implementation determines paths solely based
>> >> on the destination address.
>> >>
>> >> -vlad
>> >>
>> >>>
>> >>> First of all, we are using iproute2 to form 2 table such that when
>> >>> IP-B arrives on IP-X, it will know how to route back to IP-B on the
>> >>> same interface, i.e (eth1). Same logic for the path "IP-A to IP-X".
>> >>>
>> >>> What we observed here is that when 12.1.1.1 sends INIT to 11.1.1.11,
>> >>> LKSCTP will send back the INIT_ACK to 12.1.1.1 using 12.1.1.11 but not
>> >>> using the IP 11.1.1.11.
>> >>>
>> >>> The above operation makes the subsequence HB/HB_ACK in using wrong IP address.
>> >>>
>> >>> TCP trace on eth1
>> >>> 18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>> >>> [init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>> >>> 18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>> >>> 18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>> >>> 18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>> >>> 18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>> >>> 18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>> >>> 18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>> >>>
>> >>> TCP trace on eth2
>> >>> 18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>> >>> [init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>> >>> 3340756356]
>> >>> 18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>> >>> 18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>> >>> 18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>> >>> 18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>> >>> 18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>> >>> 18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>> >>> 18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>> >>> 18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>> >>> 18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>> >>>
>> >>>
>> >>> If we are using single homing, there is no problem on the SCTP
>> >>> communication. Below is the TCP trace on eth1 using sctp_test
>> >>>
>> >>> 18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>> >>> [init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>> >>> 18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>> >>> [init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16] [init TSN:
>> >>> 1877695021]
>> >>> 18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>> >>> 18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>> >>> 18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>> >>> 18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>> >>> 18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [DATA]
>> >>> (B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
>> >>> 18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [SACK]
>> >>> [cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
>> >>> 18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>> >>> 18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>> >>>
>> >>> From the observations, it seems that the LKSCTP library is not able to
>> >>> use the original local address when multi-homing is being used. Is
>> >>> there anyway can be resolved it?
>> >>>
>> >>> Thanks
>> >>>
>> >>> PS
>> >>> --
>> >>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>> >>> the body of a message to majordomo@vger.kernel.org
>> >>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>> >>>
>> >>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>

Re: Supporting 4 way connections in LKSCTP

[Vlad Yasevich]

On 11/27/2013 11:03 PM, Sun Paul wrote:
> How LKSCTP select which source address to use for the INIT_ACK or
> HB_ACK? below is the testing result where a router is located in the
> middle.
> 
> Before starting the application. the packet on eth1 and eth2 are
> 
> eth1
> 0 packets dropped by kernel
> [root@localhost ~]# tcpdump -i eth1 -s 0 -nn
> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
> listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
> 11:24:14.262489 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
> [init tag: 28362903] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
> 11:24:14.262522 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
> 11:24:14.539486
> 11:24:16.262488 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
> [init tag: 29391734] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
> 11:24:16.262520 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
> 
> eth2
> [root@localhost ~]# tcpdump -i eth2 -s 0 -nn
> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
> listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes
> 
> When starting the application. the packet show as below.
> 
> eth1
> 11:26:02.261511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
> [init tag: 26256828] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
> 11:26:02.263513 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [COOKIE ECHO]
> 11:26:02.264518 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
> 11:26:02.563511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
> 
> eth2
> 11:26:02.261604 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
> [init tag: 3478239387] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
> 2330749678]
> 11:26:02.263583 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
> 11:26:02.264548 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
> 11:26:02.264652 IP 11.1.1.1.2905 > 120.1.1.1.2905: sctp (1) [HB REQ]
> 11:26:02.264705 IP 120.1.1.1.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
> 11:26:02.563543 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
> 
> From the above result, you can see that the INIT, COOKIE ECHO and
> HB_REQ originated from 12.1.1.1 on eth1, but the ACK (INIT_ACK,
> COOKIE_ACK, HB_ACK) are returned on eth2 using source address
> 120.1.1.1 instead of 110.1.1.1.
> 
> Why LKSCTP use 120.1.1.1 as source instead of 110.1.1.1?
> 
> For simple ICMP ping test, it is normal, but not for SCTP.
> 
> eth1
> 11:30:02.824548 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
> seq 12, length 64
> 11:30:02.824559 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
> seq 12, length 64
> 11:30:03.825551 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
> seq 13, length 64
> 11:30:03.825561 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
> seq 13, length 64
> 
> eth2
> 11:30:34.027687 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
> seq 2, length 64
> 11:30:34.027697 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
> seq 2, length 64
> 11:30:35.027686 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
> seq 3, length 64
> 11:30:35.027694 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
> seq 3, length 64
> 
> Below is the route information
> #route -n
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
> 110.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth1
> 120.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth2
> 
> # ip route show
> 110.1.1.0/24 dev eth1  proto kernel  scope link  src 110.1.1.1
> 120.1.1.0/24 dev eth2  proto kernel  scope link  src 120.1.1.1
> 
> Since we are using iproute2, so we will have dedicate routing table
> per interface
> 
> # ip route show table SCTP1
> default via 110.1.1.254 dev eth1
> 
> # ip route show table SCTP2
> default via 120.1.1.254 dev eth2
> 
> # ip rule ls
> 0: from all lookup local
> 101: from 110.1.1.1 lookup SCTP1
> 102: from 120.1.1.1 lookup SCTP2
> 32766: from all lookup main
> 32767: from all lookup default
> 
> How LKSCTP select source address to reply? If we know how it works,
> then we may know what is going wrong.

LKSCTP will prefer the address returned from the routing table as long
as it is one of the addresses that is bound by the socket and are usable
by the association.

If the address returned from the route lookup is not part of the
association, then lksctp attempts to lookup routes using one of the
source addresses it has available.  Usually the first lookup succeeds
due to the host-model implementation in linux.

You may want to change your rule set to be destination based.  Then
in the table associated with the rule, specify the source address
you want to be used.

-vlad
> 
> On Wed, Nov 27, 2013 at 8:45 PM, Neil Horman <nhorman@tuxdriver.com> wrote:
>> On Wed, Nov 27, 2013 at 07:10:49AM +0800, Sun Paul wrote:
>>> Hi Vlad
>>>
>>> Thank for your reply. If it is based on the destination IP to find the
>>> best route, why the problem didn't happen on single-homing sample?
>>>
>> Because You only ever use one address from NODE A (12.1.1.1)
>>
>>> In the single-homing sample that provided in the original email, both
>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>> test. However, the LKSCTP library know to use the interface eth1 to
>>> respond to the SCTP request.
>>>
>> Yes, because it does a route lookup to each of the two ip addresses to NODE B,
>> and in both lookups, the route indicates that only one source address should be
>> used (12.1.1.1).  If you issue a ip route show command, you'll see that routes
>> to both address on NODE B match on a rule that specifies the same src address
>> and interface be used.
>>
>> Neil
>>
>>> - PS
>>>
>>> On Wed, Nov 27, 2013 at 7:09 AM, Sun Paul <paulrbk@gmail.com> wrote:
>>>> Hi Vlad
>>>>
>>>> Thank for your reply. If it is based on the destination IP to find the
>>>> best route, why the problem didn't happen on single-homing sample?
>>>>
>>>> In the single-homing sample that provided in the original email, both
>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>> respond to the SCTP request.
>>>>
>>>> - PS
>>>>
>>>> On Tue, Nov 26, 2013 at 11:19 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>>> On 11/25/2013 08:03 PM, Sun Paul wrote:
>>>>>> Hi
>>>>>>
>>>>>> we have a problem on using LKSCTP to form a 4 ways multi-homing network.
>>>>>>
>>>>>> Configuration
>>>>>> - Node-A has 2 IP addresses in different subnets, known as IP-A (eth1),
>>>>>> IP-B (eth2)
>>>>>> - Node-B has 2 IP addresses in different subnets, known as IP-X (eth1),
>>>>>> IP-Y (eth2)
>>>>>>
>>>>>
>>>>> First of all, this is not a 4 way multi-homed network.  As far as each
>>>>> SCTP association is concerned, it has only 2 destinations to send to
>>>>> so it has only 2 ways to get there.  The fact that you have multiple
>>>>> local addresses doesn't mean that every local address can and should
>>>>> be used to connect to the remote.
>>>>>
>>>>>> the four way paths are shown below.
>>>>>> 1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
>>>>>> 2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
>>>>>> 3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
>>>>>> 4. IP-B (12.1.1.1) to IP-X (11.1.1.11)
>>>>>
>>>>> No, actually you only have 2 paths:  one to IPX and one to IP-Y.
>>>>> Which source address you choose is based on routing policy
>>>>> decisions and is outside the scope of SCTP.
>>>>>
>>>>>>
>>>>>> the HB/HB_ACK is normal for the paths " IP-A to IP-X" and "IP-B to
>>>>>> IP-Y", but it is not correct for the rest of two.
>>>>>
>>>>> Right, because linux is using a host addressing model, not an interface
>>>>> addressing model.  SCTP stack simply finds the best source address
>>>>> that can be used to reach IP-X and it happens to be IP-A.  So that
>>>>> is what it is going to use.
>>>>>
>>>>> The above explains why you are seeing what you describe below.
>>>>>
>>>>> In the end, linux SCTP implementation determines paths solely based
>>>>> on the destination address.
>>>>>
>>>>> -vlad
>>>>>
>>>>>>
>>>>>> First of all, we are using iproute2 to form 2 table such that when
>>>>>> IP-B arrives on IP-X, it will know how to route back to IP-B on the
>>>>>> same interface, i.e (eth1). Same logic for the path "IP-A to IP-X".
>>>>>>
>>>>>> What we observed here is that when 12.1.1.1 sends INIT to 11.1.1.11,
>>>>>> LKSCTP will send back the INIT_ACK to 12.1.1.1 using 12.1.1.11 but not
>>>>>> using the IP 11.1.1.11.
>>>>>>
>>>>>> The above operation makes the subsequence HB/HB_ACK in using wrong IP address.
>>>>>>
>>>>>> TCP trace on eth1
>>>>>> 18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>> [init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>> 18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>> 18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>> 18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>> 18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>> 18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>> 18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>
>>>>>> TCP trace on eth2
>>>>>> 18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>> [init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>>> 3340756356]
>>>>>> 18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>> 18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>> 18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>> 18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>> 18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>> 18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>> 18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>> 18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>> 18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>
>>>>>>
>>>>>> If we are using single homing, there is no problem on the SCTP
>>>>>> communication. Below is the TCP trace on eth1 using sctp_test
>>>>>>
>>>>>> 18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>> [init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>> 18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>> [init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16] [init TSN:
>>>>>> 1877695021]
>>>>>> 18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>> 18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>> 18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>> 18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>> 18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [DATA]
>>>>>> (B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
>>>>>> 18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [SACK]
>>>>>> [cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
>>>>>> 18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>> 18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>
>>>>>> From the observations, it seems that the LKSCTP library is not able to
>>>>>> use the original local address when multi-homing is being used. Is
>>>>>> there anyway can be resolved it?
>>>>>>
>>>>>> Thanks
>>>>>>
>>>>>> PS
>>>>>> --
>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>
>>>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>

Re: Supporting 4 way connections in LKSCTP

[Karl Heiss]

On Mon, Dec 2, 2013 at 9:38 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
> On 11/27/2013 11:03 PM, Sun Paul wrote:
>> How LKSCTP select which source address to use for the INIT_ACK or
>> HB_ACK? below is the testing result where a router is located in the
>> middle.
>>
>> Before starting the application. the packet on eth1 and eth2 are
>>
>> eth1
>> 0 packets dropped by kernel
>> [root@localhost ~]# tcpdump -i eth1 -s 0 -nn
>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>> listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
>> 11:24:14.262489 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>> [init tag: 28362903] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>> 11:24:14.262522 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>> 11:24:14.539486
>> 11:24:16.262488 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>> [init tag: 29391734] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>> 11:24:16.262520 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>
>> eth2
>> [root@localhost ~]# tcpdump -i eth2 -s 0 -nn
>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>> listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes
>>
>> When starting the application. the packet show as below.
>>
>> eth1
>> 11:26:02.261511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>> [init tag: 26256828] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>> 11:26:02.263513 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [COOKIE ECHO]
>> 11:26:02.264518 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>> 11:26:02.563511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>
>> eth2
>> 11:26:02.261604 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>> [init tag: 3478239387] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>> 2330749678]
>> 11:26:02.263583 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>> 11:26:02.264548 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>> 11:26:02.264652 IP 11.1.1.1.2905 > 120.1.1.1.2905: sctp (1) [HB REQ]
>> 11:26:02.264705 IP 120.1.1.1.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>> 11:26:02.563543 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>
>> From the above result, you can see that the INIT, COOKIE ECHO and
>> HB_REQ originated from 12.1.1.1 on eth1, but the ACK (INIT_ACK,
>> COOKIE_ACK, HB_ACK) are returned on eth2 using source address
>> 120.1.1.1 instead of 110.1.1.1.
>>
>> Why LKSCTP use 120.1.1.1 as source instead of 110.1.1.1?
>>
>> For simple ICMP ping test, it is normal, but not for SCTP.
>>
>> eth1
>> 11:30:02.824548 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>> seq 12, length 64
>> 11:30:02.824559 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>> seq 12, length 64
>> 11:30:03.825551 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>> seq 13, length 64
>> 11:30:03.825561 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>> seq 13, length 64
>>
>> eth2
>> 11:30:34.027687 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>> seq 2, length 64
>> 11:30:34.027697 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>> seq 2, length 64
>> 11:30:35.027686 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>> seq 3, length 64
>> 11:30:35.027694 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>> seq 3, length 64
>>
>> Below is the route information
>> #route -n
>> Kernel IP routing table
>> Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
>> 110.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth1
>> 120.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth2
>>
>> # ip route show
>> 110.1.1.0/24 dev eth1  proto kernel  scope link  src 110.1.1.1
>> 120.1.1.0/24 dev eth2  proto kernel  scope link  src 120.1.1.1
>>
>> Since we are using iproute2, so we will have dedicate routing table
>> per interface
>>
>> # ip route show table SCTP1
>> default via 110.1.1.254 dev eth1
>>
>> # ip route show table SCTP2
>> default via 120.1.1.254 dev eth2
>>
>> # ip rule ls
>> 0: from all lookup local
>> 101: from 110.1.1.1 lookup SCTP1
>> 102: from 120.1.1.1 lookup SCTP2
>> 32766: from all lookup main
>> 32767: from all lookup default
>>
>> How LKSCTP select source address to reply? If we know how it works,
>> then we may know what is going wrong.
>
> LKSCTP will prefer the address returned from the routing table as long
> as it is one of the addresses that is bound by the socket and are usable
> by the association.
>
> If the address returned from the route lookup is not part of the
> association, then lksctp attempts to lookup routes using one of the
> source addresses it has available.  Usually the first lookup succeeds
> due to the host-model implementation in linux.
>
> You may want to change your rule set to be destination based.  Then
> in the table associated with the rule, specify the source address
> you want to be used.
>
> -vlad

I have had similar qualms myself about this behavior, and I honestly
don't know what the correct answer should be...

In my opinion, shouldn't the source address "just work" for
acknowledgements? If the spec explicitly states that the ACK should
have a source address that matches the destination of the chunk being
ACKed, why should someone have to configure this behavior outside of
the SCTP stack by default? Is it a technical limitation, or is this
done for a particular reason?  I can understand needing to override
the behavior, but why isn't the default "sane"?

Karl

>>
>> On Wed, Nov 27, 2013 at 8:45 PM, Neil Horman <nhorman@tuxdriver.com> wrote:
>>> On Wed, Nov 27, 2013 at 07:10:49AM +0800, Sun Paul wrote:
>>>> Hi Vlad
>>>>
>>>> Thank for your reply. If it is based on the destination IP to find the
>>>> best route, why the problem didn't happen on single-homing sample?
>>>>
>>> Because You only ever use one address from NODE A (12.1.1.1)
>>>
>>>> In the single-homing sample that provided in the original email, both
>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>> respond to the SCTP request.
>>>>
>>> Yes, because it does a route lookup to each of the two ip addresses to NODE B,
>>> and in both lookups, the route indicates that only one source address should be
>>> used (12.1.1.1).  If you issue a ip route show command, you'll see that routes
>>> to both address on NODE B match on a rule that specifies the same src address
>>> and interface be used.
>>>
>>> Neil
>>>
>>>> - PS
>>>>
>>>> On Wed, Nov 27, 2013 at 7:09 AM, Sun Paul <paulrbk@gmail.com> wrote:
>>>>> Hi Vlad
>>>>>
>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>
>>>>> In the single-homing sample that provided in the original email, both
>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>> respond to the SCTP request.
>>>>>
>>>>> - PS
>>>>>
>>>>> On Tue, Nov 26, 2013 at 11:19 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>>>> On 11/25/2013 08:03 PM, Sun Paul wrote:
>>>>>>> Hi
>>>>>>>
>>>>>>> we have a problem on using LKSCTP to form a 4 ways multi-homing network.
>>>>>>>
>>>>>>> Configuration
>>>>>>> - Node-A has 2 IP addresses in different subnets, known as IP-A (eth1),
>>>>>>> IP-B (eth2)
>>>>>>> - Node-B has 2 IP addresses in different subnets, known as IP-X (eth1),
>>>>>>> IP-Y (eth2)
>>>>>>>
>>>>>>
>>>>>> First of all, this is not a 4 way multi-homed network.  As far as each
>>>>>> SCTP association is concerned, it has only 2 destinations to send to
>>>>>> so it has only 2 ways to get there.  The fact that you have multiple
>>>>>> local addresses doesn't mean that every local address can and should
>>>>>> be used to connect to the remote.
>>>>>>
>>>>>>> the four way paths are shown below.
>>>>>>> 1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
>>>>>>> 2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
>>>>>>> 3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
>>>>>>> 4. IP-B (12.1.1.1) to IP-X (11.1.1.11)
>>>>>>
>>>>>> No, actually you only have 2 paths:  one to IPX and one to IP-Y.
>>>>>> Which source address you choose is based on routing policy
>>>>>> decisions and is outside the scope of SCTP.
>>>>>>
>>>>>>>
>>>>>>> the HB/HB_ACK is normal for the paths " IP-A to IP-X" and "IP-B to
>>>>>>> IP-Y", but it is not correct for the rest of two.
>>>>>>
>>>>>> Right, because linux is using a host addressing model, not an interface
>>>>>> addressing model.  SCTP stack simply finds the best source address
>>>>>> that can be used to reach IP-X and it happens to be IP-A.  So that
>>>>>> is what it is going to use.
>>>>>>
>>>>>> The above explains why you are seeing what you describe below.
>>>>>>
>>>>>> In the end, linux SCTP implementation determines paths solely based
>>>>>> on the destination address.
>>>>>>
>>>>>> -vlad
>>>>>>
>>>>>>>
>>>>>>> First of all, we are using iproute2 to form 2 table such that when
>>>>>>> IP-B arrives on IP-X, it will know how to route back to IP-B on the
>>>>>>> same interface, i.e (eth1). Same logic for the path "IP-A to IP-X".
>>>>>>>
>>>>>>> What we observed here is that when 12.1.1.1 sends INIT to 11.1.1.11,
>>>>>>> LKSCTP will send back the INIT_ACK to 12.1.1.1 using 12.1.1.11 but not
>>>>>>> using the IP 11.1.1.11.
>>>>>>>
>>>>>>> The above operation makes the subsequence HB/HB_ACK in using wrong IP address.
>>>>>>>
>>>>>>> TCP trace on eth1
>>>>>>> 18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>> [init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>> 18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>> 18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>> 18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>> 18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>> 18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>> 18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>
>>>>>>> TCP trace on eth2
>>>>>>> 18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>> [init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>>>> 3340756356]
>>>>>>> 18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>> 18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>> 18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>> 18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>> 18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>> 18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>> 18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>> 18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>> 18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>
>>>>>>>
>>>>>>> If we are using single homing, there is no problem on the SCTP
>>>>>>> communication. Below is the TCP trace on eth1 using sctp_test
>>>>>>>
>>>>>>> 18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>> [init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>> 18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>> [init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16] [init TSN:
>>>>>>> 1877695021]
>>>>>>> 18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>> 18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>> 18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>> 18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>> 18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [DATA]
>>>>>>> (B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
>>>>>>> 18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [SACK]
>>>>>>> [cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
>>>>>>> 18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>> 18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>
>>>>>>> From the observations, it seems that the LKSCTP library is not able to
>>>>>>> use the original local address when multi-homing is being used. Is
>>>>>>> there anyway can be resolved it?
>>>>>>>
>>>>>>> Thanks
>>>>>>>
>>>>>>> PS
>>>>>>> --
>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>>
>>>>>>
>>>> --
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>>>>
>
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Re: Supporting 4 way connections in LKSCTP

[Vlad Yasevich]

On 12/02/2013 10:45 AM, Karl Heiss wrote:
> On Mon, Dec 2, 2013 at 9:38 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>> On 11/27/2013 11:03 PM, Sun Paul wrote:
>>> How LKSCTP select which source address to use for the INIT_ACK or
>>> HB_ACK? below is the testing result where a router is located in the
>>> middle.
>>>
>>> Before starting the application. the packet on eth1 and eth2 are
>>>
>>> eth1
>>> 0 packets dropped by kernel
>>> [root@localhost ~]# tcpdump -i eth1 -s 0 -nn
>>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>>> listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
>>> 11:24:14.262489 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>> [init tag: 28362903] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>> 11:24:14.262522 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>> 11:24:14.539486
>>> 11:24:16.262488 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>> [init tag: 29391734] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>> 11:24:16.262520 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>>
>>> eth2
>>> [root@localhost ~]# tcpdump -i eth2 -s 0 -nn
>>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>>> listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes
>>>
>>> When starting the application. the packet show as below.
>>>
>>> eth1
>>> 11:26:02.261511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>> [init tag: 26256828] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>> 11:26:02.263513 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [COOKIE ECHO]
>>> 11:26:02.264518 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>> 11:26:02.563511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>>
>>> eth2
>>> 11:26:02.261604 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>> [init tag: 3478239387] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>> 2330749678]
>>> 11:26:02.263583 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>> 11:26:02.264548 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>> 11:26:02.264652 IP 11.1.1.1.2905 > 120.1.1.1.2905: sctp (1) [HB REQ]
>>> 11:26:02.264705 IP 120.1.1.1.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>> 11:26:02.563543 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>
>>> From the above result, you can see that the INIT, COOKIE ECHO and
>>> HB_REQ originated from 12.1.1.1 on eth1, but the ACK (INIT_ACK,
>>> COOKIE_ACK, HB_ACK) are returned on eth2 using source address
>>> 120.1.1.1 instead of 110.1.1.1.
>>>
>>> Why LKSCTP use 120.1.1.1 as source instead of 110.1.1.1?
>>>
>>> For simple ICMP ping test, it is normal, but not for SCTP.
>>>
>>> eth1
>>> 11:30:02.824548 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>>> seq 12, length 64
>>> 11:30:02.824559 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>>> seq 12, length 64
>>> 11:30:03.825551 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>>> seq 13, length 64
>>> 11:30:03.825561 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>>> seq 13, length 64
>>>
>>> eth2
>>> 11:30:34.027687 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>>> seq 2, length 64
>>> 11:30:34.027697 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>>> seq 2, length 64
>>> 11:30:35.027686 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>>> seq 3, length 64
>>> 11:30:35.027694 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>>> seq 3, length 64
>>>
>>> Below is the route information
>>> #route -n
>>> Kernel IP routing table
>>> Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
>>> 110.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth1
>>> 120.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth2
>>>
>>> # ip route show
>>> 110.1.1.0/24 dev eth1  proto kernel  scope link  src 110.1.1.1
>>> 120.1.1.0/24 dev eth2  proto kernel  scope link  src 120.1.1.1
>>>
>>> Since we are using iproute2, so we will have dedicate routing table
>>> per interface
>>>
>>> # ip route show table SCTP1
>>> default via 110.1.1.254 dev eth1
>>>
>>> # ip route show table SCTP2
>>> default via 120.1.1.254 dev eth2
>>>
>>> # ip rule ls
>>> 0: from all lookup local
>>> 101: from 110.1.1.1 lookup SCTP1
>>> 102: from 120.1.1.1 lookup SCTP2
>>> 32766: from all lookup main
>>> 32767: from all lookup default
>>>
>>> How LKSCTP select source address to reply? If we know how it works,
>>> then we may know what is going wrong.
>>
>> LKSCTP will prefer the address returned from the routing table as long
>> as it is one of the addresses that is bound by the socket and are usable
>> by the association.
>>
>> If the address returned from the route lookup is not part of the
>> association, then lksctp attempts to lookup routes using one of the
>> source addresses it has available.  Usually the first lookup succeeds
>> due to the host-model implementation in linux.
>>
>> You may want to change your rule set to be destination based.  Then
>> in the table associated with the rule, specify the source address
>> you want to be used.
>>
>> -vlad
> 
> I have had similar qualms myself about this behavior, and I honestly
> don't know what the correct answer should be...
> 
> In my opinion, shouldn't the source address "just work" for
> acknowledgements? If the spec explicitly states that the ACK should
> have a source address that matches the destination of the chunk being
> ACKed, why should someone have to configure this behavior outside of
> the SCTP stack by default? Is it a technical limitation, or is this
> done for a particular reason?  I can understand needing to override
> the behavior, but why isn't the default "sane"?

I think the results are sane, they simply may not match expectations.
SCTP spec doesn't say anything about source address selection.  It
says that a response should be send back to the source of the request.
This is being done in both cases, i.e. the destination address in
INIT-ACK matches the source of the INIT.

The spec does contain the MAY text that allows finer control of source
addresses, but lksctp doesn't seem to implement that.  Whenever we've
tried, we couldn't get the generic mechanism working to please everyone,
as everyone had slightly different configurations and expectations.  So
we left it to the rules engine.

In this setup, it just appears that the default routing is not what you
expect.  You can easily check this with 'ip route get' command.  If it
is not what you want linux allows you to change that via ip rules.

-vlad

> 
> Karl
> 
>>>
>>> On Wed, Nov 27, 2013 at 8:45 PM, Neil Horman <nhorman@tuxdriver.com> wrote:
>>>> On Wed, Nov 27, 2013 at 07:10:49AM +0800, Sun Paul wrote:
>>>>> Hi Vlad
>>>>>
>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>
>>>> Because You only ever use one address from NODE A (12.1.1.1)
>>>>
>>>>> In the single-homing sample that provided in the original email, both
>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>> respond to the SCTP request.
>>>>>
>>>> Yes, because it does a route lookup to each of the two ip addresses to NODE B,
>>>> and in both lookups, the route indicates that only one source address should be
>>>> used (12.1.1.1).  If you issue a ip route show command, you'll see that routes
>>>> to both address on NODE B match on a rule that specifies the same src address
>>>> and interface be used.
>>>>
>>>> Neil
>>>>
>>>>> - PS
>>>>>
>>>>> On Wed, Nov 27, 2013 at 7:09 AM, Sun Paul <paulrbk@gmail.com> wrote:
>>>>>> Hi Vlad
>>>>>>
>>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>>
>>>>>> In the single-homing sample that provided in the original email, both
>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>>> respond to the SCTP request.
>>>>>>
>>>>>> - PS
>>>>>>
>>>>>> On Tue, Nov 26, 2013 at 11:19 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>>>>> On 11/25/2013 08:03 PM, Sun Paul wrote:
>>>>>>>> Hi
>>>>>>>>
>>>>>>>> we have a problem on using LKSCTP to form a 4 ways multi-homing network.
>>>>>>>>
>>>>>>>> Configuration
>>>>>>>> - Node-A has 2 IP addresses in different subnets, known as IP-A (eth1),
>>>>>>>> IP-B (eth2)
>>>>>>>> - Node-B has 2 IP addresses in different subnets, known as IP-X (eth1),
>>>>>>>> IP-Y (eth2)
>>>>>>>>
>>>>>>>
>>>>>>> First of all, this is not a 4 way multi-homed network.  As far as each
>>>>>>> SCTP association is concerned, it has only 2 destinations to send to
>>>>>>> so it has only 2 ways to get there.  The fact that you have multiple
>>>>>>> local addresses doesn't mean that every local address can and should
>>>>>>> be used to connect to the remote.
>>>>>>>
>>>>>>>> the four way paths are shown below.
>>>>>>>> 1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
>>>>>>>> 2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>> 3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>> 4. IP-B (12.1.1.1) to IP-X (11.1.1.11)
>>>>>>>
>>>>>>> No, actually you only have 2 paths:  one to IPX and one to IP-Y.
>>>>>>> Which source address you choose is based on routing policy
>>>>>>> decisions and is outside the scope of SCTP.
>>>>>>>
>>>>>>>>
>>>>>>>> the HB/HB_ACK is normal for the paths " IP-A to IP-X" and "IP-B to
>>>>>>>> IP-Y", but it is not correct for the rest of two.
>>>>>>>
>>>>>>> Right, because linux is using a host addressing model, not an interface
>>>>>>> addressing model.  SCTP stack simply finds the best source address
>>>>>>> that can be used to reach IP-X and it happens to be IP-A.  So that
>>>>>>> is what it is going to use.
>>>>>>>
>>>>>>> The above explains why you are seeing what you describe below.
>>>>>>>
>>>>>>> In the end, linux SCTP implementation determines paths solely based
>>>>>>> on the destination address.
>>>>>>>
>>>>>>> -vlad
>>>>>>>
>>>>>>>>
>>>>>>>> First of all, we are using iproute2 to form 2 table such that when
>>>>>>>> IP-B arrives on IP-X, it will know how to route back to IP-B on the
>>>>>>>> same interface, i.e (eth1). Same logic for the path "IP-A to IP-X".
>>>>>>>>
>>>>>>>> What we observed here is that when 12.1.1.1 sends INIT to 11.1.1.11,
>>>>>>>> LKSCTP will send back the INIT_ACK to 12.1.1.1 using 12.1.1.11 but not
>>>>>>>> using the IP 11.1.1.11.
>>>>>>>>
>>>>>>>> The above operation makes the subsequence HB/HB_ACK in using wrong IP address.
>>>>>>>>
>>>>>>>> TCP trace on eth1
>>>>>>>> 18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>>> [init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>> 18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>>> 18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>> 18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>> 18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>> 18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>> 18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>
>>>>>>>> TCP trace on eth2
>>>>>>>> 18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>> [init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>>>>> 3340756356]
>>>>>>>> 18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>> 18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>> 18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>> 18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>> 18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>> 18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>> 18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>> 18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>> 18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>
>>>>>>>>
>>>>>>>> If we are using single homing, there is no problem on the SCTP
>>>>>>>> communication. Below is the TCP trace on eth1 using sctp_test
>>>>>>>>
>>>>>>>> 18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>>> [init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>> 18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>> [init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16] [init TSN:
>>>>>>>> 1877695021]
>>>>>>>> 18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>>> 18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>> 18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>> 18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>> 18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [DATA]
>>>>>>>> (B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
>>>>>>>> 18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [SACK]
>>>>>>>> [cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
>>>>>>>> 18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>> 18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>
>>>>>>>> From the observations, it seems that the LKSCTP library is not able to
>>>>>>>> use the original local address when multi-homing is being used. Is
>>>>>>>> there anyway can be resolved it?
>>>>>>>>
>>>>>>>> Thanks
>>>>>>>>
>>>>>>>> PS
>>>>>>>> --
>>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>>>
>>>>>>>
>>>>> --
>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>> the body of a message to majordomo@vger.kernel.org
>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>
>>
>> --
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Re: Supporting 4 way connections in LKSCTP

[Karl Heiss]

On Mon, Dec 2, 2013 at 11:42 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
> On 12/02/2013 10:45 AM, Karl Heiss wrote:
>> On Mon, Dec 2, 2013 at 9:38 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>> On 11/27/2013 11:03 PM, Sun Paul wrote:
>>>> How LKSCTP select which source address to use for the INIT_ACK or
>>>> HB_ACK? below is the testing result where a router is located in the
>>>> middle.
>>>>
>>>> Before starting the application. the packet on eth1 and eth2 are
>>>>
>>>> eth1
>>>> 0 packets dropped by kernel
>>>> [root@localhost ~]# tcpdump -i eth1 -s 0 -nn
>>>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>>>> listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
>>>> 11:24:14.262489 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>> [init tag: 28362903] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>> 11:24:14.262522 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>>> 11:24:14.539486
>>>> 11:24:16.262488 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>> [init tag: 29391734] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>> 11:24:16.262520 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>>>
>>>> eth2
>>>> [root@localhost ~]# tcpdump -i eth2 -s 0 -nn
>>>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>>>> listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes
>>>>
>>>> When starting the application. the packet show as below.
>>>>
>>>> eth1
>>>> 11:26:02.261511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>> [init tag: 26256828] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>> 11:26:02.263513 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [COOKIE ECHO]
>>>> 11:26:02.264518 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>>> 11:26:02.563511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>>>
>>>> eth2
>>>> 11:26:02.261604 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>> [init tag: 3478239387] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>> 2330749678]
>>>> 11:26:02.263583 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>> 11:26:02.264548 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>> 11:26:02.264652 IP 11.1.1.1.2905 > 120.1.1.1.2905: sctp (1) [HB REQ]
>>>> 11:26:02.264705 IP 120.1.1.1.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>> 11:26:02.563543 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>
>>>> From the above result, you can see that the INIT, COOKIE ECHO and
>>>> HB_REQ originated from 12.1.1.1 on eth1, but the ACK (INIT_ACK,
>>>> COOKIE_ACK, HB_ACK) are returned on eth2 using source address
>>>> 120.1.1.1 instead of 110.1.1.1.
>>>>
>>>> Why LKSCTP use 120.1.1.1 as source instead of 110.1.1.1?
>>>>
>>>> For simple ICMP ping test, it is normal, but not for SCTP.
>>>>
>>>> eth1
>>>> 11:30:02.824548 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>>>> seq 12, length 64
>>>> 11:30:02.824559 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>>>> seq 12, length 64
>>>> 11:30:03.825551 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>>>> seq 13, length 64
>>>> 11:30:03.825561 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>>>> seq 13, length 64
>>>>
>>>> eth2
>>>> 11:30:34.027687 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>>>> seq 2, length 64
>>>> 11:30:34.027697 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>>>> seq 2, length 64
>>>> 11:30:35.027686 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>>>> seq 3, length 64
>>>> 11:30:35.027694 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>>>> seq 3, length 64
>>>>
>>>> Below is the route information
>>>> #route -n
>>>> Kernel IP routing table
>>>> Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
>>>> 110.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth1
>>>> 120.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth2
>>>>
>>>> # ip route show
>>>> 110.1.1.0/24 dev eth1  proto kernel  scope link  src 110.1.1.1
>>>> 120.1.1.0/24 dev eth2  proto kernel  scope link  src 120.1.1.1
>>>>
>>>> Since we are using iproute2, so we will have dedicate routing table
>>>> per interface
>>>>
>>>> # ip route show table SCTP1
>>>> default via 110.1.1.254 dev eth1
>>>>
>>>> # ip route show table SCTP2
>>>> default via 120.1.1.254 dev eth2
>>>>
>>>> # ip rule ls
>>>> 0: from all lookup local
>>>> 101: from 110.1.1.1 lookup SCTP1
>>>> 102: from 120.1.1.1 lookup SCTP2
>>>> 32766: from all lookup main
>>>> 32767: from all lookup default
>>>>
>>>> How LKSCTP select source address to reply? If we know how it works,
>>>> then we may know what is going wrong.
>>>
>>> LKSCTP will prefer the address returned from the routing table as long
>>> as it is one of the addresses that is bound by the socket and are usable
>>> by the association.
>>>
>>> If the address returned from the route lookup is not part of the
>>> association, then lksctp attempts to lookup routes using one of the
>>> source addresses it has available.  Usually the first lookup succeeds
>>> due to the host-model implementation in linux.
>>>
>>> You may want to change your rule set to be destination based.  Then
>>> in the table associated with the rule, specify the source address
>>> you want to be used.
>>>
>>> -vlad
>>
>> I have had similar qualms myself about this behavior, and I honestly
>> don't know what the correct answer should be...
>>
>> In my opinion, shouldn't the source address "just work" for
>> acknowledgements? If the spec explicitly states that the ACK should
>> have a source address that matches the destination of the chunk being
>> ACKed, why should someone have to configure this behavior outside of
>> the SCTP stack by default? Is it a technical limitation, or is this
>> done for a particular reason?  I can understand needing to override
>> the behavior, but why isn't the default "sane"?
>
> I think the results are sane, they simply may not match expectations.
> SCTP spec doesn't say anything about source address selection.  It
> says that a response should be send back to the source of the request.
> This is being done in both cases, i.e. the destination address in
> INIT-ACK matches the source of the INIT.
>
> The spec does contain the MAY text that allows finer control of source
> addresses, but lksctp doesn't seem to implement that.  Whenever we've
> tried, we couldn't get the generic mechanism working to please everyone,
> as everyone had slightly different configurations and expectations.  So
> we left it to the rules engine.
>

Oops!  You are correct.  I must have accidentally read it as a SHOULD.. ;-)

Thanks for the history on previous attempts.  I had always wondered about this.

Karl

> In this setup, it just appears that the default routing is not what you
> expect.  You can easily check this with 'ip route get' command.  If it
> is not what you want linux allows you to change that via ip rules.
>
> -vlad
>
>>
>> Karl
>>
>>>>
>>>> On Wed, Nov 27, 2013 at 8:45 PM, Neil Horman <nhorman@tuxdriver.com> wrote:
>>>>> On Wed, Nov 27, 2013 at 07:10:49AM +0800, Sun Paul wrote:
>>>>>> Hi Vlad
>>>>>>
>>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>>
>>>>> Because You only ever use one address from NODE A (12.1.1.1)
>>>>>
>>>>>> In the single-homing sample that provided in the original email, both
>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>>> respond to the SCTP request.
>>>>>>
>>>>> Yes, because it does a route lookup to each of the two ip addresses to NODE B,
>>>>> and in both lookups, the route indicates that only one source address should be
>>>>> used (12.1.1.1).  If you issue a ip route show command, you'll see that routes
>>>>> to both address on NODE B match on a rule that specifies the same src address
>>>>> and interface be used.
>>>>>
>>>>> Neil
>>>>>
>>>>>> - PS
>>>>>>
>>>>>> On Wed, Nov 27, 2013 at 7:09 AM, Sun Paul <paulrbk@gmail.com> wrote:
>>>>>>> Hi Vlad
>>>>>>>
>>>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>>>
>>>>>>> In the single-homing sample that provided in the original email, both
>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>>>> respond to the SCTP request.
>>>>>>>
>>>>>>> - PS
>>>>>>>
>>>>>>> On Tue, Nov 26, 2013 at 11:19 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>>>>>> On 11/25/2013 08:03 PM, Sun Paul wrote:
>>>>>>>>> Hi
>>>>>>>>>
>>>>>>>>> we have a problem on using LKSCTP to form a 4 ways multi-homing network.
>>>>>>>>>
>>>>>>>>> Configuration
>>>>>>>>> - Node-A has 2 IP addresses in different subnets, known as IP-A (eth1),
>>>>>>>>> IP-B (eth2)
>>>>>>>>> - Node-B has 2 IP addresses in different subnets, known as IP-X (eth1),
>>>>>>>>> IP-Y (eth2)
>>>>>>>>>
>>>>>>>>
>>>>>>>> First of all, this is not a 4 way multi-homed network.  As far as each
>>>>>>>> SCTP association is concerned, it has only 2 destinations to send to
>>>>>>>> so it has only 2 ways to get there.  The fact that you have multiple
>>>>>>>> local addresses doesn't mean that every local address can and should
>>>>>>>> be used to connect to the remote.
>>>>>>>>
>>>>>>>>> the four way paths are shown below.
>>>>>>>>> 1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>> 2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>> 3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>> 4. IP-B (12.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>
>>>>>>>> No, actually you only have 2 paths:  one to IPX and one to IP-Y.
>>>>>>>> Which source address you choose is based on routing policy
>>>>>>>> decisions and is outside the scope of SCTP.
>>>>>>>>
>>>>>>>>>
>>>>>>>>> the HB/HB_ACK is normal for the paths " IP-A to IP-X" and "IP-B to
>>>>>>>>> IP-Y", but it is not correct for the rest of two.
>>>>>>>>
>>>>>>>> Right, because linux is using a host addressing model, not an interface
>>>>>>>> addressing model.  SCTP stack simply finds the best source address
>>>>>>>> that can be used to reach IP-X and it happens to be IP-A.  So that
>>>>>>>> is what it is going to use.
>>>>>>>>
>>>>>>>> The above explains why you are seeing what you describe below.
>>>>>>>>
>>>>>>>> In the end, linux SCTP implementation determines paths solely based
>>>>>>>> on the destination address.
>>>>>>>>
>>>>>>>> -vlad
>>>>>>>>
>>>>>>>>>
>>>>>>>>> First of all, we are using iproute2 to form 2 table such that when
>>>>>>>>> IP-B arrives on IP-X, it will know how to route back to IP-B on the
>>>>>>>>> same interface, i.e (eth1). Same logic for the path "IP-A to IP-X".
>>>>>>>>>
>>>>>>>>> What we observed here is that when 12.1.1.1 sends INIT to 11.1.1.11,
>>>>>>>>> LKSCTP will send back the INIT_ACK to 12.1.1.1 using 12.1.1.11 but not
>>>>>>>>> using the IP 11.1.1.11.
>>>>>>>>>
>>>>>>>>> The above operation makes the subsequence HB/HB_ACK in using wrong IP address.
>>>>>>>>>
>>>>>>>>> TCP trace on eth1
>>>>>>>>> 18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>>>> [init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>>> 18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>>>> 18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>> 18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>> 18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>> 18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>
>>>>>>>>> TCP trace on eth2
>>>>>>>>> 18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>>> [init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>>>>>> 3340756356]
>>>>>>>>> 18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>>> 18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>> 18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> If we are using single homing, there is no problem on the SCTP
>>>>>>>>> communication. Below is the TCP trace on eth1 using sctp_test
>>>>>>>>>
>>>>>>>>> 18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>>>> [init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>>> 18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>>> [init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16] [init TSN:
>>>>>>>>> 1877695021]
>>>>>>>>> 18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>>>> 18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>>> 18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>> 18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [DATA]
>>>>>>>>> (B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
>>>>>>>>> 18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [SACK]
>>>>>>>>> [cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
>>>>>>>>> 18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>
>>>>>>>>> From the observations, it seems that the LKSCTP library is not able to
>>>>>>>>> use the original local address when multi-homing is being used. Is
>>>>>>>>> there anyway can be resolved it?
>>>>>>>>>
>>>>>>>>> Thanks
>>>>>>>>>
>>>>>>>>> PS
>>>>>>>>> --
>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>>>>
>>>>>>>>
>>>>>> --
>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>
>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>

Re: Supporting 4 way connections in LKSCTP

[Sun Paul]

Thanks Vlad

I checked on the route, and it looks correct.

[root@localhost ~]# ip route get 11.1.1.1 from 110.1.1.1
11.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
    cache  mtu 1500 advmss 1460 hoplimit 64

[root@localhost ~]# ip route get 11.1.1.1 from 120.1.1.1
11.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
    cache  mtu 1500 advmss 1460 hoplimit 64

[root@localhost ~]# ip route get 12.1.1.1 from 120.1.1.1
12.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
    cache  mtu 1500 advmss 1460 hoplimit 64

[root@localhost ~]# ip route get 12.1.1.1 from 110.1.1.1
12.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
    cache  mtu 1500 advmss 1460 hoplimit 64

so, if this is not being handled in LKSCTP, is it possible to suggest
a way how we can achieve it?

On Tue, Dec 3, 2013 at 12:42 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
> On 12/02/2013 10:45 AM, Karl Heiss wrote:
>> On Mon, Dec 2, 2013 at 9:38 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>> On 11/27/2013 11:03 PM, Sun Paul wrote:
>>>> How LKSCTP select which source address to use for the INIT_ACK or
>>>> HB_ACK? below is the testing result where a router is located in the
>>>> middle.
>>>>
>>>> Before starting the application. the packet on eth1 and eth2 are
>>>>
>>>> eth1
>>>> 0 packets dropped by kernel
>>>> [root@localhost ~]# tcpdump -i eth1 -s 0 -nn
>>>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>>>> listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
>>>> 11:24:14.262489 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>> [init tag: 28362903] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>> 11:24:14.262522 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>>> 11:24:14.539486
>>>> 11:24:16.262488 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>> [init tag: 29391734] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>> 11:24:16.262520 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>>>
>>>> eth2
>>>> [root@localhost ~]# tcpdump -i eth2 -s 0 -nn
>>>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>>>> listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes
>>>>
>>>> When starting the application. the packet show as below.
>>>>
>>>> eth1
>>>> 11:26:02.261511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>> [init tag: 26256828] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>> 11:26:02.263513 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [COOKIE ECHO]
>>>> 11:26:02.264518 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>>> 11:26:02.563511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>>>
>>>> eth2
>>>> 11:26:02.261604 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>> [init tag: 3478239387] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>> 2330749678]
>>>> 11:26:02.263583 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>> 11:26:02.264548 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>> 11:26:02.264652 IP 11.1.1.1.2905 > 120.1.1.1.2905: sctp (1) [HB REQ]
>>>> 11:26:02.264705 IP 120.1.1.1.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>> 11:26:02.563543 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>
>>>> From the above result, you can see that the INIT, COOKIE ECHO and
>>>> HB_REQ originated from 12.1.1.1 on eth1, but the ACK (INIT_ACK,
>>>> COOKIE_ACK, HB_ACK) are returned on eth2 using source address
>>>> 120.1.1.1 instead of 110.1.1.1.
>>>>
>>>> Why LKSCTP use 120.1.1.1 as source instead of 110.1.1.1?
>>>>
>>>> For simple ICMP ping test, it is normal, but not for SCTP.
>>>>
>>>> eth1
>>>> 11:30:02.824548 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>>>> seq 12, length 64
>>>> 11:30:02.824559 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>>>> seq 12, length 64
>>>> 11:30:03.825551 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>>>> seq 13, length 64
>>>> 11:30:03.825561 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>>>> seq 13, length 64
>>>>
>>>> eth2
>>>> 11:30:34.027687 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>>>> seq 2, length 64
>>>> 11:30:34.027697 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>>>> seq 2, length 64
>>>> 11:30:35.027686 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>>>> seq 3, length 64
>>>> 11:30:35.027694 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>>>> seq 3, length 64
>>>>
>>>> Below is the route information
>>>> #route -n
>>>> Kernel IP routing table
>>>> Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
>>>> 110.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth1
>>>> 120.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth2
>>>>
>>>> # ip route show
>>>> 110.1.1.0/24 dev eth1  proto kernel  scope link  src 110.1.1.1
>>>> 120.1.1.0/24 dev eth2  proto kernel  scope link  src 120.1.1.1
>>>>
>>>> Since we are using iproute2, so we will have dedicate routing table
>>>> per interface
>>>>
>>>> # ip route show table SCTP1
>>>> default via 110.1.1.254 dev eth1
>>>>
>>>> # ip route show table SCTP2
>>>> default via 120.1.1.254 dev eth2
>>>>
>>>> # ip rule ls
>>>> 0: from all lookup local
>>>> 101: from 110.1.1.1 lookup SCTP1
>>>> 102: from 120.1.1.1 lookup SCTP2
>>>> 32766: from all lookup main
>>>> 32767: from all lookup default
>>>>
>>>> How LKSCTP select source address to reply? If we know how it works,
>>>> then we may know what is going wrong.
>>>
>>> LKSCTP will prefer the address returned from the routing table as long
>>> as it is one of the addresses that is bound by the socket and are usable
>>> by the association.
>>>
>>> If the address returned from the route lookup is not part of the
>>> association, then lksctp attempts to lookup routes using one of the
>>> source addresses it has available.  Usually the first lookup succeeds
>>> due to the host-model implementation in linux.
>>>
>>> You may want to change your rule set to be destination based.  Then
>>> in the table associated with the rule, specify the source address
>>> you want to be used.
>>>
>>> -vlad
>>
>> I have had similar qualms myself about this behavior, and I honestly
>> don't know what the correct answer should be...
>>
>> In my opinion, shouldn't the source address "just work" for
>> acknowledgements? If the spec explicitly states that the ACK should
>> have a source address that matches the destination of the chunk being
>> ACKed, why should someone have to configure this behavior outside of
>> the SCTP stack by default? Is it a technical limitation, or is this
>> done for a particular reason?  I can understand needing to override
>> the behavior, but why isn't the default "sane"?
>
> I think the results are sane, they simply may not match expectations.
> SCTP spec doesn't say anything about source address selection.  It
> says that a response should be send back to the source of the request.
> This is being done in both cases, i.e. the destination address in
> INIT-ACK matches the source of the INIT.
>
> The spec does contain the MAY text that allows finer control of source
> addresses, but lksctp doesn't seem to implement that.  Whenever we've
> tried, we couldn't get the generic mechanism working to please everyone,
> as everyone had slightly different configurations and expectations.  So
> we left it to the rules engine.
>
> In this setup, it just appears that the default routing is not what you
> expect.  You can easily check this with 'ip route get' command.  If it
> is not what you want linux allows you to change that via ip rules.
>
> -vlad
>
>>
>> Karl
>>
>>>>
>>>> On Wed, Nov 27, 2013 at 8:45 PM, Neil Horman <nhorman@tuxdriver.com> wrote:
>>>>> On Wed, Nov 27, 2013 at 07:10:49AM +0800, Sun Paul wrote:
>>>>>> Hi Vlad
>>>>>>
>>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>>
>>>>> Because You only ever use one address from NODE A (12.1.1.1)
>>>>>
>>>>>> In the single-homing sample that provided in the original email, both
>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>>> respond to the SCTP request.
>>>>>>
>>>>> Yes, because it does a route lookup to each of the two ip addresses to NODE B,
>>>>> and in both lookups, the route indicates that only one source address should be
>>>>> used (12.1.1.1).  If you issue a ip route show command, you'll see that routes
>>>>> to both address on NODE B match on a rule that specifies the same src address
>>>>> and interface be used.
>>>>>
>>>>> Neil
>>>>>
>>>>>> - PS
>>>>>>
>>>>>> On Wed, Nov 27, 2013 at 7:09 AM, Sun Paul <paulrbk@gmail.com> wrote:
>>>>>>> Hi Vlad
>>>>>>>
>>>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>>>
>>>>>>> In the single-homing sample that provided in the original email, both
>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>>>> respond to the SCTP request.
>>>>>>>
>>>>>>> - PS
>>>>>>>
>>>>>>> On Tue, Nov 26, 2013 at 11:19 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>>>>>> On 11/25/2013 08:03 PM, Sun Paul wrote:
>>>>>>>>> Hi
>>>>>>>>>
>>>>>>>>> we have a problem on using LKSCTP to form a 4 ways multi-homing network.
>>>>>>>>>
>>>>>>>>> Configuration
>>>>>>>>> - Node-A has 2 IP addresses in different subnets, known as IP-A (eth1),
>>>>>>>>> IP-B (eth2)
>>>>>>>>> - Node-B has 2 IP addresses in different subnets, known as IP-X (eth1),
>>>>>>>>> IP-Y (eth2)
>>>>>>>>>
>>>>>>>>
>>>>>>>> First of all, this is not a 4 way multi-homed network.  As far as each
>>>>>>>> SCTP association is concerned, it has only 2 destinations to send to
>>>>>>>> so it has only 2 ways to get there.  The fact that you have multiple
>>>>>>>> local addresses doesn't mean that every local address can and should
>>>>>>>> be used to connect to the remote.
>>>>>>>>
>>>>>>>>> the four way paths are shown below.
>>>>>>>>> 1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>> 2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>> 3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>> 4. IP-B (12.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>
>>>>>>>> No, actually you only have 2 paths:  one to IPX and one to IP-Y.
>>>>>>>> Which source address you choose is based on routing policy
>>>>>>>> decisions and is outside the scope of SCTP.
>>>>>>>>
>>>>>>>>>
>>>>>>>>> the HB/HB_ACK is normal for the paths " IP-A to IP-X" and "IP-B to
>>>>>>>>> IP-Y", but it is not correct for the rest of two.
>>>>>>>>
>>>>>>>> Right, because linux is using a host addressing model, not an interface
>>>>>>>> addressing model.  SCTP stack simply finds the best source address
>>>>>>>> that can be used to reach IP-X and it happens to be IP-A.  So that
>>>>>>>> is what it is going to use.
>>>>>>>>
>>>>>>>> The above explains why you are seeing what you describe below.
>>>>>>>>
>>>>>>>> In the end, linux SCTP implementation determines paths solely based
>>>>>>>> on the destination address.
>>>>>>>>
>>>>>>>> -vlad
>>>>>>>>
>>>>>>>>>
>>>>>>>>> First of all, we are using iproute2 to form 2 table such that when
>>>>>>>>> IP-B arrives on IP-X, it will know how to route back to IP-B on the
>>>>>>>>> same interface, i.e (eth1). Same logic for the path "IP-A to IP-X".
>>>>>>>>>
>>>>>>>>> What we observed here is that when 12.1.1.1 sends INIT to 11.1.1.11,
>>>>>>>>> LKSCTP will send back the INIT_ACK to 12.1.1.1 using 12.1.1.11 but not
>>>>>>>>> using the IP 11.1.1.11.
>>>>>>>>>
>>>>>>>>> The above operation makes the subsequence HB/HB_ACK in using wrong IP address.
>>>>>>>>>
>>>>>>>>> TCP trace on eth1
>>>>>>>>> 18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>>>> [init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>>> 18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>>>> 18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>> 18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>> 18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>> 18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>
>>>>>>>>> TCP trace on eth2
>>>>>>>>> 18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>>> [init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>>>>>> 3340756356]
>>>>>>>>> 18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>>> 18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>> 18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> If we are using single homing, there is no problem on the SCTP
>>>>>>>>> communication. Below is the TCP trace on eth1 using sctp_test
>>>>>>>>>
>>>>>>>>> 18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>>>> [init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>>> 18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>>> [init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16] [init TSN:
>>>>>>>>> 1877695021]
>>>>>>>>> 18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>>>> 18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>>> 18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>> 18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [DATA]
>>>>>>>>> (B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
>>>>>>>>> 18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [SACK]
>>>>>>>>> [cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
>>>>>>>>> 18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>> 18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>
>>>>>>>>> From the observations, it seems that the LKSCTP library is not able to
>>>>>>>>> use the original local address when multi-homing is being used. Is
>>>>>>>>> there anyway can be resolved it?
>>>>>>>>>
>>>>>>>>> Thanks
>>>>>>>>>
>>>>>>>>> PS
>>>>>>>>> --
>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>>>>
>>>>>>>>
>>>>>> --
>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>
>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>

Re: Supporting 4 way connections in LKSCTP

[Sun Paul]

Another question

if a wrong source IP is used, does the association still classified as normal?

On Tue, Dec 3, 2013 at 9:31 AM, Sun Paul <paulrbk@gmail.com> wrote:
> Thanks Vlad
>
> I checked on the route, and it looks correct.
>
> [root@localhost ~]# ip route get 11.1.1.1 from 110.1.1.1
> 11.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
>     cache  mtu 1500 advmss 1460 hoplimit 64
>
> [root@localhost ~]# ip route get 11.1.1.1 from 120.1.1.1
> 11.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
>     cache  mtu 1500 advmss 1460 hoplimit 64
>
> [root@localhost ~]# ip route get 12.1.1.1 from 120.1.1.1
> 12.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
>     cache  mtu 1500 advmss 1460 hoplimit 64
>
> [root@localhost ~]# ip route get 12.1.1.1 from 110.1.1.1
> 12.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
>     cache  mtu 1500 advmss 1460 hoplimit 64
>
> so, if this is not being handled in LKSCTP, is it possible to suggest
> a way how we can achieve it?
>
> On Tue, Dec 3, 2013 at 12:42 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>> On 12/02/2013 10:45 AM, Karl Heiss wrote:
>>> On Mon, Dec 2, 2013 at 9:38 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>> On 11/27/2013 11:03 PM, Sun Paul wrote:
>>>>> How LKSCTP select which source address to use for the INIT_ACK or
>>>>> HB_ACK? below is the testing result where a router is located in the
>>>>> middle.
>>>>>
>>>>> Before starting the application. the packet on eth1 and eth2 are
>>>>>
>>>>> eth1
>>>>> 0 packets dropped by kernel
>>>>> [root@localhost ~]# tcpdump -i eth1 -s 0 -nn
>>>>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>>>>> listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
>>>>> 11:24:14.262489 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>> [init tag: 28362903] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>> 11:24:14.262522 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>>>> 11:24:14.539486
>>>>> 11:24:16.262488 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>> [init tag: 29391734] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>> 11:24:16.262520 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>>>>
>>>>> eth2
>>>>> [root@localhost ~]# tcpdump -i eth2 -s 0 -nn
>>>>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>>>>> listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes
>>>>>
>>>>> When starting the application. the packet show as below.
>>>>>
>>>>> eth1
>>>>> 11:26:02.261511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>> [init tag: 26256828] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>> 11:26:02.263513 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [COOKIE ECHO]
>>>>> 11:26:02.264518 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>>>> 11:26:02.563511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>>>>
>>>>> eth2
>>>>> 11:26:02.261604 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>> [init tag: 3478239387] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>> 2330749678]
>>>>> 11:26:02.263583 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>> 11:26:02.264548 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>> 11:26:02.264652 IP 11.1.1.1.2905 > 120.1.1.1.2905: sctp (1) [HB REQ]
>>>>> 11:26:02.264705 IP 120.1.1.1.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>> 11:26:02.563543 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>
>>>>> From the above result, you can see that the INIT, COOKIE ECHO and
>>>>> HB_REQ originated from 12.1.1.1 on eth1, but the ACK (INIT_ACK,
>>>>> COOKIE_ACK, HB_ACK) are returned on eth2 using source address
>>>>> 120.1.1.1 instead of 110.1.1.1.
>>>>>
>>>>> Why LKSCTP use 120.1.1.1 as source instead of 110.1.1.1?
>>>>>
>>>>> For simple ICMP ping test, it is normal, but not for SCTP.
>>>>>
>>>>> eth1
>>>>> 11:30:02.824548 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>>>>> seq 12, length 64
>>>>> 11:30:02.824559 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>>>>> seq 12, length 64
>>>>> 11:30:03.825551 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>>>>> seq 13, length 64
>>>>> 11:30:03.825561 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>>>>> seq 13, length 64
>>>>>
>>>>> eth2
>>>>> 11:30:34.027687 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>>>>> seq 2, length 64
>>>>> 11:30:34.027697 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>>>>> seq 2, length 64
>>>>> 11:30:35.027686 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>>>>> seq 3, length 64
>>>>> 11:30:35.027694 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>>>>> seq 3, length 64
>>>>>
>>>>> Below is the route information
>>>>> #route -n
>>>>> Kernel IP routing table
>>>>> Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
>>>>> 110.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth1
>>>>> 120.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth2
>>>>>
>>>>> # ip route show
>>>>> 110.1.1.0/24 dev eth1  proto kernel  scope link  src 110.1.1.1
>>>>> 120.1.1.0/24 dev eth2  proto kernel  scope link  src 120.1.1.1
>>>>>
>>>>> Since we are using iproute2, so we will have dedicate routing table
>>>>> per interface
>>>>>
>>>>> # ip route show table SCTP1
>>>>> default via 110.1.1.254 dev eth1
>>>>>
>>>>> # ip route show table SCTP2
>>>>> default via 120.1.1.254 dev eth2
>>>>>
>>>>> # ip rule ls
>>>>> 0: from all lookup local
>>>>> 101: from 110.1.1.1 lookup SCTP1
>>>>> 102: from 120.1.1.1 lookup SCTP2
>>>>> 32766: from all lookup main
>>>>> 32767: from all lookup default
>>>>>
>>>>> How LKSCTP select source address to reply? If we know how it works,
>>>>> then we may know what is going wrong.
>>>>
>>>> LKSCTP will prefer the address returned from the routing table as long
>>>> as it is one of the addresses that is bound by the socket and are usable
>>>> by the association.
>>>>
>>>> If the address returned from the route lookup is not part of the
>>>> association, then lksctp attempts to lookup routes using one of the
>>>> source addresses it has available.  Usually the first lookup succeeds
>>>> due to the host-model implementation in linux.
>>>>
>>>> You may want to change your rule set to be destination based.  Then
>>>> in the table associated with the rule, specify the source address
>>>> you want to be used.
>>>>
>>>> -vlad
>>>
>>> I have had similar qualms myself about this behavior, and I honestly
>>> don't know what the correct answer should be...
>>>
>>> In my opinion, shouldn't the source address "just work" for
>>> acknowledgements? If the spec explicitly states that the ACK should
>>> have a source address that matches the destination of the chunk being
>>> ACKed, why should someone have to configure this behavior outside of
>>> the SCTP stack by default? Is it a technical limitation, or is this
>>> done for a particular reason?  I can understand needing to override
>>> the behavior, but why isn't the default "sane"?
>>
>> I think the results are sane, they simply may not match expectations.
>> SCTP spec doesn't say anything about source address selection.  It
>> says that a response should be send back to the source of the request.
>> This is being done in both cases, i.e. the destination address in
>> INIT-ACK matches the source of the INIT.
>>
>> The spec does contain the MAY text that allows finer control of source
>> addresses, but lksctp doesn't seem to implement that.  Whenever we've
>> tried, we couldn't get the generic mechanism working to please everyone,
>> as everyone had slightly different configurations and expectations.  So
>> we left it to the rules engine.
>>
>> In this setup, it just appears that the default routing is not what you
>> expect.  You can easily check this with 'ip route get' command.  If it
>> is not what you want linux allows you to change that via ip rules.
>>
>> -vlad
>>
>>>
>>> Karl
>>>
>>>>>
>>>>> On Wed, Nov 27, 2013 at 8:45 PM, Neil Horman <nhorman@tuxdriver.com> wrote:
>>>>>> On Wed, Nov 27, 2013 at 07:10:49AM +0800, Sun Paul wrote:
>>>>>>> Hi Vlad
>>>>>>>
>>>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>>>
>>>>>> Because You only ever use one address from NODE A (12.1.1.1)
>>>>>>
>>>>>>> In the single-homing sample that provided in the original email, both
>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>>>> respond to the SCTP request.
>>>>>>>
>>>>>> Yes, because it does a route lookup to each of the two ip addresses to NODE B,
>>>>>> and in both lookups, the route indicates that only one source address should be
>>>>>> used (12.1.1.1).  If you issue a ip route show command, you'll see that routes
>>>>>> to both address on NODE B match on a rule that specifies the same src address
>>>>>> and interface be used.
>>>>>>
>>>>>> Neil
>>>>>>
>>>>>>> - PS
>>>>>>>
>>>>>>> On Wed, Nov 27, 2013 at 7:09 AM, Sun Paul <paulrbk@gmail.com> wrote:
>>>>>>>> Hi Vlad
>>>>>>>>
>>>>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>>>>
>>>>>>>> In the single-homing sample that provided in the original email, both
>>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>>>>> respond to the SCTP request.
>>>>>>>>
>>>>>>>> - PS
>>>>>>>>
>>>>>>>> On Tue, Nov 26, 2013 at 11:19 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>>>>>>> On 11/25/2013 08:03 PM, Sun Paul wrote:
>>>>>>>>>> Hi
>>>>>>>>>>
>>>>>>>>>> we have a problem on using LKSCTP to form a 4 ways multi-homing network.
>>>>>>>>>>
>>>>>>>>>> Configuration
>>>>>>>>>> - Node-A has 2 IP addresses in different subnets, known as IP-A (eth1),
>>>>>>>>>> IP-B (eth2)
>>>>>>>>>> - Node-B has 2 IP addresses in different subnets, known as IP-X (eth1),
>>>>>>>>>> IP-Y (eth2)
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> First of all, this is not a 4 way multi-homed network.  As far as each
>>>>>>>>> SCTP association is concerned, it has only 2 destinations to send to
>>>>>>>>> so it has only 2 ways to get there.  The fact that you have multiple
>>>>>>>>> local addresses doesn't mean that every local address can and should
>>>>>>>>> be used to connect to the remote.
>>>>>>>>>
>>>>>>>>>> the four way paths are shown below.
>>>>>>>>>> 1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>>> 2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>>> 3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>>> 4. IP-B (12.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>>
>>>>>>>>> No, actually you only have 2 paths:  one to IPX and one to IP-Y.
>>>>>>>>> Which source address you choose is based on routing policy
>>>>>>>>> decisions and is outside the scope of SCTP.
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> the HB/HB_ACK is normal for the paths " IP-A to IP-X" and "IP-B to
>>>>>>>>>> IP-Y", but it is not correct for the rest of two.
>>>>>>>>>
>>>>>>>>> Right, because linux is using a host addressing model, not an interface
>>>>>>>>> addressing model.  SCTP stack simply finds the best source address
>>>>>>>>> that can be used to reach IP-X and it happens to be IP-A.  So that
>>>>>>>>> is what it is going to use.
>>>>>>>>>
>>>>>>>>> The above explains why you are seeing what you describe below.
>>>>>>>>>
>>>>>>>>> In the end, linux SCTP implementation determines paths solely based
>>>>>>>>> on the destination address.
>>>>>>>>>
>>>>>>>>> -vlad
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> First of all, we are using iproute2 to form 2 table such that when
>>>>>>>>>> IP-B arrives on IP-X, it will know how to route back to IP-B on the
>>>>>>>>>> same interface, i.e (eth1). Same logic for the path "IP-A to IP-X".
>>>>>>>>>>
>>>>>>>>>> What we observed here is that when 12.1.1.1 sends INIT to 11.1.1.11,
>>>>>>>>>> LKSCTP will send back the INIT_ACK to 12.1.1.1 using 12.1.1.11 but not
>>>>>>>>>> using the IP 11.1.1.11.
>>>>>>>>>>
>>>>>>>>>> The above operation makes the subsequence HB/HB_ACK in using wrong IP address.
>>>>>>>>>>
>>>>>>>>>> TCP trace on eth1
>>>>>>>>>> 18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>>>>> [init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>>>> 18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>>>>> 18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>> 18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>> 18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>> 18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>> 18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>
>>>>>>>>>> TCP trace on eth2
>>>>>>>>>> 18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>>>> [init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>>>>>>> 3340756356]
>>>>>>>>>> 18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>>>> 18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>> 18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>> 18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>> 18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>> 18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>> 18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>> 18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>> 18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> If we are using single homing, there is no problem on the SCTP
>>>>>>>>>> communication. Below is the TCP trace on eth1 using sctp_test
>>>>>>>>>>
>>>>>>>>>> 18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>>>>> [init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>>>> 18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>>>> [init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16] [init TSN:
>>>>>>>>>> 1877695021]
>>>>>>>>>> 18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>>>>> 18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>>>> 18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>> 18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>> 18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [DATA]
>>>>>>>>>> (B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
>>>>>>>>>> 18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [SACK]
>>>>>>>>>> [cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
>>>>>>>>>> 18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>> 18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>
>>>>>>>>>> From the observations, it seems that the LKSCTP library is not able to
>>>>>>>>>> use the original local address when multi-homing is being used. Is
>>>>>>>>>> there anyway can be resolved it?
>>>>>>>>>>
>>>>>>>>>> Thanks
>>>>>>>>>>
>>>>>>>>>> PS
>>>>>>>>>> --
>>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>>>>>
>>>>>>>>>
>>>>>>> --
>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>>
>>>>
>>>> --
>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>> the body of a message to majordomo@vger.kernel.org
>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>

Re: Supporting 4 way connections in LKSCTP

[Vlad Yasevich]

On 12/02/2013 08:31 PM, Sun Paul wrote:
> Thanks Vlad
> 
> I checked on the route, and it looks correct.
> 
> [root@localhost ~]# ip route get 11.1.1.1 from 110.1.1.1
> 11.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
>     cache  mtu 1500 advmss 1460 hoplimit 64
> 
> [root@localhost ~]# ip route get 11.1.1.1 from 120.1.1.1
> 11.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
>     cache  mtu 1500 advmss 1460 hoplimit 64
> 
> [root@localhost ~]# ip route get 12.1.1.1 from 120.1.1.1
> 12.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
>     cache  mtu 1500 advmss 1460 hoplimit 64
> 
> [root@localhost ~]# ip route get 12.1.1.1 from 110.1.1.1
> 12.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
>     cache  mtu 1500 advmss 1460 hoplimit 64
> 
> so, if this is not being handled in LKSCTP, is it possible to suggest
> a way how we can achieve it?

Like I said before lksctp only iterates over the bound address
list if the source address from the route returned by the kernel
does not match the bound address list.

To simulate the algorithm with with ip route get, you'd
get something like this:

   ip route get 11.1.1.1
   if from_address not in bound address list
       for each bound_addr in bound address list
           ip route get 11.1.1.1 from bound_addr

The kernel will almost always give you a valid route even if the
from address does not belong to the expected interface.

So, in your case, what does a simple ip route get 11.1.1.1 return?
That's the address that will be used to talk to 11.1.1.1 by default.

-vlad
> 
> On Tue, Dec 3, 2013 at 12:42 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>> On 12/02/2013 10:45 AM, Karl Heiss wrote:
>>> On Mon, Dec 2, 2013 at 9:38 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>> On 11/27/2013 11:03 PM, Sun Paul wrote:
>>>>> How LKSCTP select which source address to use for the INIT_ACK or
>>>>> HB_ACK? below is the testing result where a router is located in the
>>>>> middle.
>>>>>
>>>>> Before starting the application. the packet on eth1 and eth2 are
>>>>>
>>>>> eth1
>>>>> 0 packets dropped by kernel
>>>>> [root@localhost ~]# tcpdump -i eth1 -s 0 -nn
>>>>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>>>>> listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
>>>>> 11:24:14.262489 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>> [init tag: 28362903] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>> 11:24:14.262522 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>>>> 11:24:14.539486
>>>>> 11:24:16.262488 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>> [init tag: 29391734] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>> 11:24:16.262520 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>>>>
>>>>> eth2
>>>>> [root@localhost ~]# tcpdump -i eth2 -s 0 -nn
>>>>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>>>>> listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes
>>>>>
>>>>> When starting the application. the packet show as below.
>>>>>
>>>>> eth1
>>>>> 11:26:02.261511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>> [init tag: 26256828] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>> 11:26:02.263513 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [COOKIE ECHO]
>>>>> 11:26:02.264518 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>>>> 11:26:02.563511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>>>>
>>>>> eth2
>>>>> 11:26:02.261604 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>> [init tag: 3478239387] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>> 2330749678]
>>>>> 11:26:02.263583 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>> 11:26:02.264548 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>> 11:26:02.264652 IP 11.1.1.1.2905 > 120.1.1.1.2905: sctp (1) [HB REQ]
>>>>> 11:26:02.264705 IP 120.1.1.1.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>> 11:26:02.563543 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>
>>>>> From the above result, you can see that the INIT, COOKIE ECHO and
>>>>> HB_REQ originated from 12.1.1.1 on eth1, but the ACK (INIT_ACK,
>>>>> COOKIE_ACK, HB_ACK) are returned on eth2 using source address
>>>>> 120.1.1.1 instead of 110.1.1.1.
>>>>>
>>>>> Why LKSCTP use 120.1.1.1 as source instead of 110.1.1.1?
>>>>>
>>>>> For simple ICMP ping test, it is normal, but not for SCTP.
>>>>>
>>>>> eth1
>>>>> 11:30:02.824548 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>>>>> seq 12, length 64
>>>>> 11:30:02.824559 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>>>>> seq 12, length 64
>>>>> 11:30:03.825551 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>>>>> seq 13, length 64
>>>>> 11:30:03.825561 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>>>>> seq 13, length 64
>>>>>
>>>>> eth2
>>>>> 11:30:34.027687 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>>>>> seq 2, length 64
>>>>> 11:30:34.027697 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>>>>> seq 2, length 64
>>>>> 11:30:35.027686 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>>>>> seq 3, length 64
>>>>> 11:30:35.027694 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>>>>> seq 3, length 64
>>>>>
>>>>> Below is the route information
>>>>> #route -n
>>>>> Kernel IP routing table
>>>>> Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
>>>>> 110.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth1
>>>>> 120.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth2
>>>>>
>>>>> # ip route show
>>>>> 110.1.1.0/24 dev eth1  proto kernel  scope link  src 110.1.1.1
>>>>> 120.1.1.0/24 dev eth2  proto kernel  scope link  src 120.1.1.1
>>>>>
>>>>> Since we are using iproute2, so we will have dedicate routing table
>>>>> per interface
>>>>>
>>>>> # ip route show table SCTP1
>>>>> default via 110.1.1.254 dev eth1
>>>>>
>>>>> # ip route show table SCTP2
>>>>> default via 120.1.1.254 dev eth2
>>>>>
>>>>> # ip rule ls
>>>>> 0: from all lookup local
>>>>> 101: from 110.1.1.1 lookup SCTP1
>>>>> 102: from 120.1.1.1 lookup SCTP2
>>>>> 32766: from all lookup main
>>>>> 32767: from all lookup default
>>>>>
>>>>> How LKSCTP select source address to reply? If we know how it works,
>>>>> then we may know what is going wrong.
>>>>
>>>> LKSCTP will prefer the address returned from the routing table as long
>>>> as it is one of the addresses that is bound by the socket and are usable
>>>> by the association.
>>>>
>>>> If the address returned from the route lookup is not part of the
>>>> association, then lksctp attempts to lookup routes using one of the
>>>> source addresses it has available.  Usually the first lookup succeeds
>>>> due to the host-model implementation in linux.
>>>>
>>>> You may want to change your rule set to be destination based.  Then
>>>> in the table associated with the rule, specify the source address
>>>> you want to be used.
>>>>
>>>> -vlad
>>>
>>> I have had similar qualms myself about this behavior, and I honestly
>>> don't know what the correct answer should be...
>>>
>>> In my opinion, shouldn't the source address "just work" for
>>> acknowledgements? If the spec explicitly states that the ACK should
>>> have a source address that matches the destination of the chunk being
>>> ACKed, why should someone have to configure this behavior outside of
>>> the SCTP stack by default? Is it a technical limitation, or is this
>>> done for a particular reason?  I can understand needing to override
>>> the behavior, but why isn't the default "sane"?
>>
>> I think the results are sane, they simply may not match expectations.
>> SCTP spec doesn't say anything about source address selection.  It
>> says that a response should be send back to the source of the request.
>> This is being done in both cases, i.e. the destination address in
>> INIT-ACK matches the source of the INIT.
>>
>> The spec does contain the MAY text that allows finer control of source
>> addresses, but lksctp doesn't seem to implement that.  Whenever we've
>> tried, we couldn't get the generic mechanism working to please everyone,
>> as everyone had slightly different configurations and expectations.  So
>> we left it to the rules engine.
>>
>> In this setup, it just appears that the default routing is not what you
>> expect.  You can easily check this with 'ip route get' command.  If it
>> is not what you want linux allows you to change that via ip rules.
>>
>> -vlad
>>
>>>
>>> Karl
>>>
>>>>>
>>>>> On Wed, Nov 27, 2013 at 8:45 PM, Neil Horman <nhorman@tuxdriver.com> wrote:
>>>>>> On Wed, Nov 27, 2013 at 07:10:49AM +0800, Sun Paul wrote:
>>>>>>> Hi Vlad
>>>>>>>
>>>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>>>
>>>>>> Because You only ever use one address from NODE A (12.1.1.1)
>>>>>>
>>>>>>> In the single-homing sample that provided in the original email, both
>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>>>> respond to the SCTP request.
>>>>>>>
>>>>>> Yes, because it does a route lookup to each of the two ip addresses to NODE B,
>>>>>> and in both lookups, the route indicates that only one source address should be
>>>>>> used (12.1.1.1).  If you issue a ip route show command, you'll see that routes
>>>>>> to both address on NODE B match on a rule that specifies the same src address
>>>>>> and interface be used.
>>>>>>
>>>>>> Neil
>>>>>>
>>>>>>> - PS
>>>>>>>
>>>>>>> On Wed, Nov 27, 2013 at 7:09 AM, Sun Paul <paulrbk@gmail.com> wrote:
>>>>>>>> Hi Vlad
>>>>>>>>
>>>>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>>>>
>>>>>>>> In the single-homing sample that provided in the original email, both
>>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>>>>> respond to the SCTP request.
>>>>>>>>
>>>>>>>> - PS
>>>>>>>>
>>>>>>>> On Tue, Nov 26, 2013 at 11:19 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>>>>>>> On 11/25/2013 08:03 PM, Sun Paul wrote:
>>>>>>>>>> Hi
>>>>>>>>>>
>>>>>>>>>> we have a problem on using LKSCTP to form a 4 ways multi-homing network.
>>>>>>>>>>
>>>>>>>>>> Configuration
>>>>>>>>>> - Node-A has 2 IP addresses in different subnets, known as IP-A (eth1),
>>>>>>>>>> IP-B (eth2)
>>>>>>>>>> - Node-B has 2 IP addresses in different subnets, known as IP-X (eth1),
>>>>>>>>>> IP-Y (eth2)
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> First of all, this is not a 4 way multi-homed network.  As far as each
>>>>>>>>> SCTP association is concerned, it has only 2 destinations to send to
>>>>>>>>> so it has only 2 ways to get there.  The fact that you have multiple
>>>>>>>>> local addresses doesn't mean that every local address can and should
>>>>>>>>> be used to connect to the remote.
>>>>>>>>>
>>>>>>>>>> the four way paths are shown below.
>>>>>>>>>> 1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>>> 2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>>> 3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>>> 4. IP-B (12.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>>
>>>>>>>>> No, actually you only have 2 paths:  one to IPX and one to IP-Y.
>>>>>>>>> Which source address you choose is based on routing policy
>>>>>>>>> decisions and is outside the scope of SCTP.
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> the HB/HB_ACK is normal for the paths " IP-A to IP-X" and "IP-B to
>>>>>>>>>> IP-Y", but it is not correct for the rest of two.
>>>>>>>>>
>>>>>>>>> Right, because linux is using a host addressing model, not an interface
>>>>>>>>> addressing model.  SCTP stack simply finds the best source address
>>>>>>>>> that can be used to reach IP-X and it happens to be IP-A.  So that
>>>>>>>>> is what it is going to use.
>>>>>>>>>
>>>>>>>>> The above explains why you are seeing what you describe below.
>>>>>>>>>
>>>>>>>>> In the end, linux SCTP implementation determines paths solely based
>>>>>>>>> on the destination address.
>>>>>>>>>
>>>>>>>>> -vlad
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> First of all, we are using iproute2 to form 2 table such that when
>>>>>>>>>> IP-B arrives on IP-X, it will know how to route back to IP-B on the
>>>>>>>>>> same interface, i.e (eth1). Same logic for the path "IP-A to IP-X".
>>>>>>>>>>
>>>>>>>>>> What we observed here is that when 12.1.1.1 sends INIT to 11.1.1.11,
>>>>>>>>>> LKSCTP will send back the INIT_ACK to 12.1.1.1 using 12.1.1.11 but not
>>>>>>>>>> using the IP 11.1.1.11.
>>>>>>>>>>
>>>>>>>>>> The above operation makes the subsequence HB/HB_ACK in using wrong IP address.
>>>>>>>>>>
>>>>>>>>>> TCP trace on eth1
>>>>>>>>>> 18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>>>>> [init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>>>> 18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>>>>> 18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>> 18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>> 18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>> 18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>> 18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>
>>>>>>>>>> TCP trace on eth2
>>>>>>>>>> 18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>>>> [init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>>>>>>> 3340756356]
>>>>>>>>>> 18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>>>> 18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>> 18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>> 18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>> 18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>> 18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>> 18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>> 18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>> 18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> If we are using single homing, there is no problem on the SCTP
>>>>>>>>>> communication. Below is the TCP trace on eth1 using sctp_test
>>>>>>>>>>
>>>>>>>>>> 18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>>>>> [init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>>>> 18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>>>> [init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16] [init TSN:
>>>>>>>>>> 1877695021]
>>>>>>>>>> 18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>>>>> 18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>>>> 18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>> 18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>> 18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [DATA]
>>>>>>>>>> (B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
>>>>>>>>>> 18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [SACK]
>>>>>>>>>> [cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
>>>>>>>>>> 18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>> 18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>
>>>>>>>>>> From the observations, it seems that the LKSCTP library is not able to
>>>>>>>>>> use the original local address when multi-homing is being used. Is
>>>>>>>>>> there anyway can be resolved it?
>>>>>>>>>>
>>>>>>>>>> Thanks
>>>>>>>>>>
>>>>>>>>>> PS
>>>>>>>>>> --
>>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>>>>>
>>>>>>>>>
>>>>>>> --
>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>>
>>>>
>>>> --
>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>> the body of a message to majordomo@vger.kernel.org
>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>

Re: Supporting 4 way connections in LKSCTP

[Vlad Yasevich]

On 12/02/2013 08:39 PM, Sun Paul wrote:
> Another question
> 
> if a wrong source IP is used, does the association still classified as normal?

What do you mean my wrong source IP?  As long as the address is part of
the association, it can be used.

-vlad

> 
> On Tue, Dec 3, 2013 at 9:31 AM, Sun Paul <paulrbk@gmail.com> wrote:
>> Thanks Vlad
>>
>> I checked on the route, and it looks correct.
>>
>> [root@localhost ~]# ip route get 11.1.1.1 from 110.1.1.1
>> 11.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>
>> [root@localhost ~]# ip route get 11.1.1.1 from 120.1.1.1
>> 11.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>
>> [root@localhost ~]# ip route get 12.1.1.1 from 120.1.1.1
>> 12.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>
>> [root@localhost ~]# ip route get 12.1.1.1 from 110.1.1.1
>> 12.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>
>> so, if this is not being handled in LKSCTP, is it possible to suggest
>> a way how we can achieve it?
>>
>> On Tue, Dec 3, 2013 at 12:42 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>> On 12/02/2013 10:45 AM, Karl Heiss wrote:
>>>> On Mon, Dec 2, 2013 at 9:38 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>>> On 11/27/2013 11:03 PM, Sun Paul wrote:
>>>>>> How LKSCTP select which source address to use for the INIT_ACK or
>>>>>> HB_ACK? below is the testing result where a router is located in the
>>>>>> middle.
>>>>>>
>>>>>> Before starting the application. the packet on eth1 and eth2 are
>>>>>>
>>>>>> eth1
>>>>>> 0 packets dropped by kernel
>>>>>> [root@localhost ~]# tcpdump -i eth1 -s 0 -nn
>>>>>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>>>>>> listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
>>>>>> 11:24:14.262489 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>> [init tag: 28362903] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>> 11:24:14.262522 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>>>>> 11:24:14.539486
>>>>>> 11:24:16.262488 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>> [init tag: 29391734] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>> 11:24:16.262520 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>>>>>
>>>>>> eth2
>>>>>> [root@localhost ~]# tcpdump -i eth2 -s 0 -nn
>>>>>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>>>>>> listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes
>>>>>>
>>>>>> When starting the application. the packet show as below.
>>>>>>
>>>>>> eth1
>>>>>> 11:26:02.261511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>> [init tag: 26256828] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>> 11:26:02.263513 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [COOKIE ECHO]
>>>>>> 11:26:02.264518 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>>>>> 11:26:02.563511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>>>>>
>>>>>> eth2
>>>>>> 11:26:02.261604 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>> [init tag: 3478239387] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>>> 2330749678]
>>>>>> 11:26:02.263583 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>> 11:26:02.264548 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>> 11:26:02.264652 IP 11.1.1.1.2905 > 120.1.1.1.2905: sctp (1) [HB REQ]
>>>>>> 11:26:02.264705 IP 120.1.1.1.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>> 11:26:02.563543 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>
>>>>>> From the above result, you can see that the INIT, COOKIE ECHO and
>>>>>> HB_REQ originated from 12.1.1.1 on eth1, but the ACK (INIT_ACK,
>>>>>> COOKIE_ACK, HB_ACK) are returned on eth2 using source address
>>>>>> 120.1.1.1 instead of 110.1.1.1.
>>>>>>
>>>>>> Why LKSCTP use 120.1.1.1 as source instead of 110.1.1.1?
>>>>>>
>>>>>> For simple ICMP ping test, it is normal, but not for SCTP.
>>>>>>
>>>>>> eth1
>>>>>> 11:30:02.824548 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>>>>>> seq 12, length 64
>>>>>> 11:30:02.824559 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>>>>>> seq 12, length 64
>>>>>> 11:30:03.825551 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>>>>>> seq 13, length 64
>>>>>> 11:30:03.825561 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>>>>>> seq 13, length 64
>>>>>>
>>>>>> eth2
>>>>>> 11:30:34.027687 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>>>>>> seq 2, length 64
>>>>>> 11:30:34.027697 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>>>>>> seq 2, length 64
>>>>>> 11:30:35.027686 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>>>>>> seq 3, length 64
>>>>>> 11:30:35.027694 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>>>>>> seq 3, length 64
>>>>>>
>>>>>> Below is the route information
>>>>>> #route -n
>>>>>> Kernel IP routing table
>>>>>> Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
>>>>>> 110.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth1
>>>>>> 120.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth2
>>>>>>
>>>>>> # ip route show
>>>>>> 110.1.1.0/24 dev eth1  proto kernel  scope link  src 110.1.1.1
>>>>>> 120.1.1.0/24 dev eth2  proto kernel  scope link  src 120.1.1.1
>>>>>>
>>>>>> Since we are using iproute2, so we will have dedicate routing table
>>>>>> per interface
>>>>>>
>>>>>> # ip route show table SCTP1
>>>>>> default via 110.1.1.254 dev eth1
>>>>>>
>>>>>> # ip route show table SCTP2
>>>>>> default via 120.1.1.254 dev eth2
>>>>>>
>>>>>> # ip rule ls
>>>>>> 0: from all lookup local
>>>>>> 101: from 110.1.1.1 lookup SCTP1
>>>>>> 102: from 120.1.1.1 lookup SCTP2
>>>>>> 32766: from all lookup main
>>>>>> 32767: from all lookup default
>>>>>>
>>>>>> How LKSCTP select source address to reply? If we know how it works,
>>>>>> then we may know what is going wrong.
>>>>>
>>>>> LKSCTP will prefer the address returned from the routing table as long
>>>>> as it is one of the addresses that is bound by the socket and are usable
>>>>> by the association.
>>>>>
>>>>> If the address returned from the route lookup is not part of the
>>>>> association, then lksctp attempts to lookup routes using one of the
>>>>> source addresses it has available.  Usually the first lookup succeeds
>>>>> due to the host-model implementation in linux.
>>>>>
>>>>> You may want to change your rule set to be destination based.  Then
>>>>> in the table associated with the rule, specify the source address
>>>>> you want to be used.
>>>>>
>>>>> -vlad
>>>>
>>>> I have had similar qualms myself about this behavior, and I honestly
>>>> don't know what the correct answer should be...
>>>>
>>>> In my opinion, shouldn't the source address "just work" for
>>>> acknowledgements? If the spec explicitly states that the ACK should
>>>> have a source address that matches the destination of the chunk being
>>>> ACKed, why should someone have to configure this behavior outside of
>>>> the SCTP stack by default? Is it a technical limitation, or is this
>>>> done for a particular reason?  I can understand needing to override
>>>> the behavior, but why isn't the default "sane"?
>>>
>>> I think the results are sane, they simply may not match expectations.
>>> SCTP spec doesn't say anything about source address selection.  It
>>> says that a response should be send back to the source of the request.
>>> This is being done in both cases, i.e. the destination address in
>>> INIT-ACK matches the source of the INIT.
>>>
>>> The spec does contain the MAY text that allows finer control of source
>>> addresses, but lksctp doesn't seem to implement that.  Whenever we've
>>> tried, we couldn't get the generic mechanism working to please everyone,
>>> as everyone had slightly different configurations and expectations.  So
>>> we left it to the rules engine.
>>>
>>> In this setup, it just appears that the default routing is not what you
>>> expect.  You can easily check this with 'ip route get' command.  If it
>>> is not what you want linux allows you to change that via ip rules.
>>>
>>> -vlad
>>>
>>>>
>>>> Karl
>>>>
>>>>>>
>>>>>> On Wed, Nov 27, 2013 at 8:45 PM, Neil Horman <nhorman@tuxdriver.com> wrote:
>>>>>>> On Wed, Nov 27, 2013 at 07:10:49AM +0800, Sun Paul wrote:
>>>>>>>> Hi Vlad
>>>>>>>>
>>>>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>>>>
>>>>>>> Because You only ever use one address from NODE A (12.1.1.1)
>>>>>>>
>>>>>>>> In the single-homing sample that provided in the original email, both
>>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>>>>> respond to the SCTP request.
>>>>>>>>
>>>>>>> Yes, because it does a route lookup to each of the two ip addresses to NODE B,
>>>>>>> and in both lookups, the route indicates that only one source address should be
>>>>>>> used (12.1.1.1).  If you issue a ip route show command, you'll see that routes
>>>>>>> to both address on NODE B match on a rule that specifies the same src address
>>>>>>> and interface be used.
>>>>>>>
>>>>>>> Neil
>>>>>>>
>>>>>>>> - PS
>>>>>>>>
>>>>>>>> On Wed, Nov 27, 2013 at 7:09 AM, Sun Paul <paulrbk@gmail.com> wrote:
>>>>>>>>> Hi Vlad
>>>>>>>>>
>>>>>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>>>>>
>>>>>>>>> In the single-homing sample that provided in the original email, both
>>>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>>>>>> respond to the SCTP request.
>>>>>>>>>
>>>>>>>>> - PS
>>>>>>>>>
>>>>>>>>> On Tue, Nov 26, 2013 at 11:19 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>>>>>>>> On 11/25/2013 08:03 PM, Sun Paul wrote:
>>>>>>>>>>> Hi
>>>>>>>>>>>
>>>>>>>>>>> we have a problem on using LKSCTP to form a 4 ways multi-homing network.
>>>>>>>>>>>
>>>>>>>>>>> Configuration
>>>>>>>>>>> - Node-A has 2 IP addresses in different subnets, known as IP-A (eth1),
>>>>>>>>>>> IP-B (eth2)
>>>>>>>>>>> - Node-B has 2 IP addresses in different subnets, known as IP-X (eth1),
>>>>>>>>>>> IP-Y (eth2)
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> First of all, this is not a 4 way multi-homed network.  As far as each
>>>>>>>>>> SCTP association is concerned, it has only 2 destinations to send to
>>>>>>>>>> so it has only 2 ways to get there.  The fact that you have multiple
>>>>>>>>>> local addresses doesn't mean that every local address can and should
>>>>>>>>>> be used to connect to the remote.
>>>>>>>>>>
>>>>>>>>>>> the four way paths are shown below.
>>>>>>>>>>> 1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>>>> 2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>>>> 3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>>>> 4. IP-B (12.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>>>
>>>>>>>>>> No, actually you only have 2 paths:  one to IPX and one to IP-Y.
>>>>>>>>>> Which source address you choose is based on routing policy
>>>>>>>>>> decisions and is outside the scope of SCTP.
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> the HB/HB_ACK is normal for the paths " IP-A to IP-X" and "IP-B to
>>>>>>>>>>> IP-Y", but it is not correct for the rest of two.
>>>>>>>>>>
>>>>>>>>>> Right, because linux is using a host addressing model, not an interface
>>>>>>>>>> addressing model.  SCTP stack simply finds the best source address
>>>>>>>>>> that can be used to reach IP-X and it happens to be IP-A.  So that
>>>>>>>>>> is what it is going to use.
>>>>>>>>>>
>>>>>>>>>> The above explains why you are seeing what you describe below.
>>>>>>>>>>
>>>>>>>>>> In the end, linux SCTP implementation determines paths solely based
>>>>>>>>>> on the destination address.
>>>>>>>>>>
>>>>>>>>>> -vlad
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> First of all, we are using iproute2 to form 2 table such that when
>>>>>>>>>>> IP-B arrives on IP-X, it will know how to route back to IP-B on the
>>>>>>>>>>> same interface, i.e (eth1). Same logic for the path "IP-A to IP-X".
>>>>>>>>>>>
>>>>>>>>>>> What we observed here is that when 12.1.1.1 sends INIT to 11.1.1.11,
>>>>>>>>>>> LKSCTP will send back the INIT_ACK to 12.1.1.1 using 12.1.1.11 but not
>>>>>>>>>>> using the IP 11.1.1.11.
>>>>>>>>>>>
>>>>>>>>>>> The above operation makes the subsequence HB/HB_ACK in using wrong IP address.
>>>>>>>>>>>
>>>>>>>>>>> TCP trace on eth1
>>>>>>>>>>> 18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>>>>>> [init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>>>>> 18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>>>>>> 18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>> 18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>> 18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>> 18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>> 18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>>
>>>>>>>>>>> TCP trace on eth2
>>>>>>>>>>> 18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>>>>> [init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>>>>>>>> 3340756356]
>>>>>>>>>>> 18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>>>>> 18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>> 18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>> 18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>> 18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>> 18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>> 18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>> 18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>> 18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> If we are using single homing, there is no problem on the SCTP
>>>>>>>>>>> communication. Below is the TCP trace on eth1 using sctp_test
>>>>>>>>>>>
>>>>>>>>>>> 18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>>>>>> [init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>>>>> 18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>>>>> [init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16] [init TSN:
>>>>>>>>>>> 1877695021]
>>>>>>>>>>> 18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>>>>>> 18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>>>>> 18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>> 18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>> 18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [DATA]
>>>>>>>>>>> (B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
>>>>>>>>>>> 18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [SACK]
>>>>>>>>>>> [cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
>>>>>>>>>>> 18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>> 18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>>
>>>>>>>>>>> From the observations, it seems that the LKSCTP library is not able to
>>>>>>>>>>> use the original local address when multi-homing is being used. Is
>>>>>>>>>>> there anyway can be resolved it?
>>>>>>>>>>>
>>>>>>>>>>> Thanks
>>>>>>>>>>>
>>>>>>>>>>> PS
>>>>>>>>>>> --
>>>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>> --
>>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>>>
>>>>>
>>>>> --
>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>> the body of a message to majordomo@vger.kernel.org
>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>

Re: Supporting 4 way connections in LKSCTP

[Sun Paul]

so in this case, says

(NODE-A) IP-B send INIT to IP-X (NODE-B), and then IP-Y (NODE-B)
returns INIT_ACK to IP-B (NODE-A)

this is also treated as a valid, am I correct?


On Tue, Dec 3, 2013 at 10:03 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
> On 12/02/2013 08:39 PM, Sun Paul wrote:
>> Another question
>>
>> if a wrong source IP is used, does the association still classified as normal?
>
> What do you mean my wrong source IP?  As long as the address is part of
> the association, it can be used.
>
> -vlad
>
>>
>> On Tue, Dec 3, 2013 at 9:31 AM, Sun Paul <paulrbk@gmail.com> wrote:
>>> Thanks Vlad
>>>
>>> I checked on the route, and it looks correct.
>>>
>>> [root@localhost ~]# ip route get 11.1.1.1 from 110.1.1.1
>>> 11.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
>>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>>
>>> [root@localhost ~]# ip route get 11.1.1.1 from 120.1.1.1
>>> 11.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
>>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>>
>>> [root@localhost ~]# ip route get 12.1.1.1 from 120.1.1.1
>>> 12.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
>>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>>
>>> [root@localhost ~]# ip route get 12.1.1.1 from 110.1.1.1
>>> 12.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
>>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>>
>>> so, if this is not being handled in LKSCTP, is it possible to suggest
>>> a way how we can achieve it?
>>>
>>> On Tue, Dec 3, 2013 at 12:42 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>> On 12/02/2013 10:45 AM, Karl Heiss wrote:
>>>>> On Mon, Dec 2, 2013 at 9:38 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>>>> On 11/27/2013 11:03 PM, Sun Paul wrote:
>>>>>>> How LKSCTP select which source address to use for the INIT_ACK or
>>>>>>> HB_ACK? below is the testing result where a router is located in the
>>>>>>> middle.
>>>>>>>
>>>>>>> Before starting the application. the packet on eth1 and eth2 are
>>>>>>>
>>>>>>> eth1
>>>>>>> 0 packets dropped by kernel
>>>>>>> [root@localhost ~]# tcpdump -i eth1 -s 0 -nn
>>>>>>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>>>>>>> listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
>>>>>>> 11:24:14.262489 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>>> [init tag: 28362903] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>> 11:24:14.262522 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>>>>>> 11:24:14.539486
>>>>>>> 11:24:16.262488 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>>> [init tag: 29391734] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>> 11:24:16.262520 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>>>>>>
>>>>>>> eth2
>>>>>>> [root@localhost ~]# tcpdump -i eth2 -s 0 -nn
>>>>>>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>>>>>>> listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes
>>>>>>>
>>>>>>> When starting the application. the packet show as below.
>>>>>>>
>>>>>>> eth1
>>>>>>> 11:26:02.261511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>>> [init tag: 26256828] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>> 11:26:02.263513 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [COOKIE ECHO]
>>>>>>> 11:26:02.264518 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>>>>>> 11:26:02.563511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>>>>>>
>>>>>>> eth2
>>>>>>> 11:26:02.261604 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>> [init tag: 3478239387] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>>>> 2330749678]
>>>>>>> 11:26:02.263583 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>> 11:26:02.264548 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>> 11:26:02.264652 IP 11.1.1.1.2905 > 120.1.1.1.2905: sctp (1) [HB REQ]
>>>>>>> 11:26:02.264705 IP 120.1.1.1.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>> 11:26:02.563543 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>
>>>>>>> From the above result, you can see that the INIT, COOKIE ECHO and
>>>>>>> HB_REQ originated from 12.1.1.1 on eth1, but the ACK (INIT_ACK,
>>>>>>> COOKIE_ACK, HB_ACK) are returned on eth2 using source address
>>>>>>> 120.1.1.1 instead of 110.1.1.1.
>>>>>>>
>>>>>>> Why LKSCTP use 120.1.1.1 as source instead of 110.1.1.1?
>>>>>>>
>>>>>>> For simple ICMP ping test, it is normal, but not for SCTP.
>>>>>>>
>>>>>>> eth1
>>>>>>> 11:30:02.824548 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>>>>>>> seq 12, length 64
>>>>>>> 11:30:02.824559 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>>>>>>> seq 12, length 64
>>>>>>> 11:30:03.825551 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>>>>>>> seq 13, length 64
>>>>>>> 11:30:03.825561 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>>>>>>> seq 13, length 64
>>>>>>>
>>>>>>> eth2
>>>>>>> 11:30:34.027687 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>>>>>>> seq 2, length 64
>>>>>>> 11:30:34.027697 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>>>>>>> seq 2, length 64
>>>>>>> 11:30:35.027686 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>>>>>>> seq 3, length 64
>>>>>>> 11:30:35.027694 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>>>>>>> seq 3, length 64
>>>>>>>
>>>>>>> Below is the route information
>>>>>>> #route -n
>>>>>>> Kernel IP routing table
>>>>>>> Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
>>>>>>> 110.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth1
>>>>>>> 120.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth2
>>>>>>>
>>>>>>> # ip route show
>>>>>>> 110.1.1.0/24 dev eth1  proto kernel  scope link  src 110.1.1.1
>>>>>>> 120.1.1.0/24 dev eth2  proto kernel  scope link  src 120.1.1.1
>>>>>>>
>>>>>>> Since we are using iproute2, so we will have dedicate routing table
>>>>>>> per interface
>>>>>>>
>>>>>>> # ip route show table SCTP1
>>>>>>> default via 110.1.1.254 dev eth1
>>>>>>>
>>>>>>> # ip route show table SCTP2
>>>>>>> default via 120.1.1.254 dev eth2
>>>>>>>
>>>>>>> # ip rule ls
>>>>>>> 0: from all lookup local
>>>>>>> 101: from 110.1.1.1 lookup SCTP1
>>>>>>> 102: from 120.1.1.1 lookup SCTP2
>>>>>>> 32766: from all lookup main
>>>>>>> 32767: from all lookup default
>>>>>>>
>>>>>>> How LKSCTP select source address to reply? If we know how it works,
>>>>>>> then we may know what is going wrong.
>>>>>>
>>>>>> LKSCTP will prefer the address returned from the routing table as long
>>>>>> as it is one of the addresses that is bound by the socket and are usable
>>>>>> by the association.
>>>>>>
>>>>>> If the address returned from the route lookup is not part of the
>>>>>> association, then lksctp attempts to lookup routes using one of the
>>>>>> source addresses it has available.  Usually the first lookup succeeds
>>>>>> due to the host-model implementation in linux.
>>>>>>
>>>>>> You may want to change your rule set to be destination based.  Then
>>>>>> in the table associated with the rule, specify the source address
>>>>>> you want to be used.
>>>>>>
>>>>>> -vlad
>>>>>
>>>>> I have had similar qualms myself about this behavior, and I honestly
>>>>> don't know what the correct answer should be...
>>>>>
>>>>> In my opinion, shouldn't the source address "just work" for
>>>>> acknowledgements? If the spec explicitly states that the ACK should
>>>>> have a source address that matches the destination of the chunk being
>>>>> ACKed, why should someone have to configure this behavior outside of
>>>>> the SCTP stack by default? Is it a technical limitation, or is this
>>>>> done for a particular reason?  I can understand needing to override
>>>>> the behavior, but why isn't the default "sane"?
>>>>
>>>> I think the results are sane, they simply may not match expectations.
>>>> SCTP spec doesn't say anything about source address selection.  It
>>>> says that a response should be send back to the source of the request.
>>>> This is being done in both cases, i.e. the destination address in
>>>> INIT-ACK matches the source of the INIT.
>>>>
>>>> The spec does contain the MAY text that allows finer control of source
>>>> addresses, but lksctp doesn't seem to implement that.  Whenever we've
>>>> tried, we couldn't get the generic mechanism working to please everyone,
>>>> as everyone had slightly different configurations and expectations.  So
>>>> we left it to the rules engine.
>>>>
>>>> In this setup, it just appears that the default routing is not what you
>>>> expect.  You can easily check this with 'ip route get' command.  If it
>>>> is not what you want linux allows you to change that via ip rules.
>>>>
>>>> -vlad
>>>>
>>>>>
>>>>> Karl
>>>>>
>>>>>>>
>>>>>>> On Wed, Nov 27, 2013 at 8:45 PM, Neil Horman <nhorman@tuxdriver.com> wrote:
>>>>>>>> On Wed, Nov 27, 2013 at 07:10:49AM +0800, Sun Paul wrote:
>>>>>>>>> Hi Vlad
>>>>>>>>>
>>>>>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>>>>>
>>>>>>>> Because You only ever use one address from NODE A (12.1.1.1)
>>>>>>>>
>>>>>>>>> In the single-homing sample that provided in the original email, both
>>>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>>>>>> respond to the SCTP request.
>>>>>>>>>
>>>>>>>> Yes, because it does a route lookup to each of the two ip addresses to NODE B,
>>>>>>>> and in both lookups, the route indicates that only one source address should be
>>>>>>>> used (12.1.1.1).  If you issue a ip route show command, you'll see that routes
>>>>>>>> to both address on NODE B match on a rule that specifies the same src address
>>>>>>>> and interface be used.
>>>>>>>>
>>>>>>>> Neil
>>>>>>>>
>>>>>>>>> - PS
>>>>>>>>>
>>>>>>>>> On Wed, Nov 27, 2013 at 7:09 AM, Sun Paul <paulrbk@gmail.com> wrote:
>>>>>>>>>> Hi Vlad
>>>>>>>>>>
>>>>>>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>>>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>>>>>>
>>>>>>>>>> In the single-homing sample that provided in the original email, both
>>>>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>>>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>>>>>>> respond to the SCTP request.
>>>>>>>>>>
>>>>>>>>>> - PS
>>>>>>>>>>
>>>>>>>>>> On Tue, Nov 26, 2013 at 11:19 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>>>>>>>>> On 11/25/2013 08:03 PM, Sun Paul wrote:
>>>>>>>>>>>> Hi
>>>>>>>>>>>>
>>>>>>>>>>>> we have a problem on using LKSCTP to form a 4 ways multi-homing network.
>>>>>>>>>>>>
>>>>>>>>>>>> Configuration
>>>>>>>>>>>> - Node-A has 2 IP addresses in different subnets, known as IP-A (eth1),
>>>>>>>>>>>> IP-B (eth2)
>>>>>>>>>>>> - Node-B has 2 IP addresses in different subnets, known as IP-X (eth1),
>>>>>>>>>>>> IP-Y (eth2)
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> First of all, this is not a 4 way multi-homed network.  As far as each
>>>>>>>>>>> SCTP association is concerned, it has only 2 destinations to send to
>>>>>>>>>>> so it has only 2 ways to get there.  The fact that you have multiple
>>>>>>>>>>> local addresses doesn't mean that every local address can and should
>>>>>>>>>>> be used to connect to the remote.
>>>>>>>>>>>
>>>>>>>>>>>> the four way paths are shown below.
>>>>>>>>>>>> 1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>>>>> 2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>>>>> 3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>>>>> 4. IP-B (12.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>>>>
>>>>>>>>>>> No, actually you only have 2 paths:  one to IPX and one to IP-Y.
>>>>>>>>>>> Which source address you choose is based on routing policy
>>>>>>>>>>> decisions and is outside the scope of SCTP.
>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> the HB/HB_ACK is normal for the paths " IP-A to IP-X" and "IP-B to
>>>>>>>>>>>> IP-Y", but it is not correct for the rest of two.
>>>>>>>>>>>
>>>>>>>>>>> Right, because linux is using a host addressing model, not an interface
>>>>>>>>>>> addressing model.  SCTP stack simply finds the best source address
>>>>>>>>>>> that can be used to reach IP-X and it happens to be IP-A.  So that
>>>>>>>>>>> is what it is going to use.
>>>>>>>>>>>
>>>>>>>>>>> The above explains why you are seeing what you describe below.
>>>>>>>>>>>
>>>>>>>>>>> In the end, linux SCTP implementation determines paths solely based
>>>>>>>>>>> on the destination address.
>>>>>>>>>>>
>>>>>>>>>>> -vlad
>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> First of all, we are using iproute2 to form 2 table such that when
>>>>>>>>>>>> IP-B arrives on IP-X, it will know how to route back to IP-B on the
>>>>>>>>>>>> same interface, i.e (eth1). Same logic for the path "IP-A to IP-X".
>>>>>>>>>>>>
>>>>>>>>>>>> What we observed here is that when 12.1.1.1 sends INIT to 11.1.1.11,
>>>>>>>>>>>> LKSCTP will send back the INIT_ACK to 12.1.1.1 using 12.1.1.11 but not
>>>>>>>>>>>> using the IP 11.1.1.11.
>>>>>>>>>>>>
>>>>>>>>>>>> The above operation makes the subsequence HB/HB_ACK in using wrong IP address.
>>>>>>>>>>>>
>>>>>>>>>>>> TCP trace on eth1
>>>>>>>>>>>> 18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>>>>>>> [init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>>>>>> 18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>>>>>>> 18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>> 18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>>> 18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>>> 18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>>> 18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>>>
>>>>>>>>>>>> TCP trace on eth2
>>>>>>>>>>>> 18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>>>>>> [init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>>>>>>>>> 3340756356]
>>>>>>>>>>>> 18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>>>>>> 18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>>> 18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>> 18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>> 18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>> 18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>> 18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>> 18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>> 18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> If we are using single homing, there is no problem on the SCTP
>>>>>>>>>>>> communication. Below is the TCP trace on eth1 using sctp_test
>>>>>>>>>>>>
>>>>>>>>>>>> 18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>>>>>>> [init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>>>>>> 18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>>>>>> [init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16] [init TSN:
>>>>>>>>>>>> 1877695021]
>>>>>>>>>>>> 18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>>>>>>> 18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>>>>>> 18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>> 18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>>> 18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [DATA]
>>>>>>>>>>>> (B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
>>>>>>>>>>>> 18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [SACK]
>>>>>>>>>>>> [cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
>>>>>>>>>>>> 18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>> 18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>>>
>>>>>>>>>>>> From the observations, it seems that the LKSCTP library is not able to
>>>>>>>>>>>> use the original local address when multi-homing is being used. Is
>>>>>>>>>>>> there anyway can be resolved it?
>>>>>>>>>>>>
>>>>>>>>>>>> Thanks
>>>>>>>>>>>>
>>>>>>>>>>>> PS
>>>>>>>>>>>> --
>>>>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>> --
>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>>>>
>>>>>>
>>>>>> --
>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>
>

Re: Supporting 4 way connections in LKSCTP

[Sun Paul]

if we do not specific the gateway, it will be a problem. One of the
reason why it is like that is due to that the server do not know which
source IP should be used to send out the query.

[root@localhost ~]# ip route get 12.1.1.1
RTNETLINK answers: Network is unreachable

[root@localhost ~]# ip route get 11.1.1.1
RTNETLINK answers: Network is unreachable


On Tue, Dec 3, 2013 at 10:02 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
> On 12/02/2013 08:31 PM, Sun Paul wrote:
>> Thanks Vlad
>>
>> I checked on the route, and it looks correct.
>>
>> [root@localhost ~]# ip route get 11.1.1.1 from 110.1.1.1
>> 11.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>
>> [root@localhost ~]# ip route get 11.1.1.1 from 120.1.1.1
>> 11.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>
>> [root@localhost ~]# ip route get 12.1.1.1 from 120.1.1.1
>> 12.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>
>> [root@localhost ~]# ip route get 12.1.1.1 from 110.1.1.1
>> 12.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>
>> so, if this is not being handled in LKSCTP, is it possible to suggest
>> a way how we can achieve it?
>
> Like I said before lksctp only iterates over the bound address
> list if the source address from the route returned by the kernel
> does not match the bound address list.
>
> To simulate the algorithm with with ip route get, you'd
> get something like this:
>
>    ip route get 11.1.1.1
>    if from_address not in bound address list
>        for each bound_addr in bound address list
>            ip route get 11.1.1.1 from bound_addr
>
> The kernel will almost always give you a valid route even if the
> from address does not belong to the expected interface.
>
> So, in your case, what does a simple ip route get 11.1.1.1 return?
> That's the address that will be used to talk to 11.1.1.1 by default.
>
> -vlad
>>
>> On Tue, Dec 3, 2013 at 12:42 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>> On 12/02/2013 10:45 AM, Karl Heiss wrote:
>>>> On Mon, Dec 2, 2013 at 9:38 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>>> On 11/27/2013 11:03 PM, Sun Paul wrote:
>>>>>> How LKSCTP select which source address to use for the INIT_ACK or
>>>>>> HB_ACK? below is the testing result where a router is located in the
>>>>>> middle.
>>>>>>
>>>>>> Before starting the application. the packet on eth1 and eth2 are
>>>>>>
>>>>>> eth1
>>>>>> 0 packets dropped by kernel
>>>>>> [root@localhost ~]# tcpdump -i eth1 -s 0 -nn
>>>>>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>>>>>> listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
>>>>>> 11:24:14.262489 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>> [init tag: 28362903] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>> 11:24:14.262522 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>>>>> 11:24:14.539486
>>>>>> 11:24:16.262488 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>> [init tag: 29391734] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>> 11:24:16.262520 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>>>>>
>>>>>> eth2
>>>>>> [root@localhost ~]# tcpdump -i eth2 -s 0 -nn
>>>>>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>>>>>> listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes
>>>>>>
>>>>>> When starting the application. the packet show as below.
>>>>>>
>>>>>> eth1
>>>>>> 11:26:02.261511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>> [init tag: 26256828] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>> 11:26:02.263513 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [COOKIE ECHO]
>>>>>> 11:26:02.264518 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>>>>> 11:26:02.563511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>>>>>
>>>>>> eth2
>>>>>> 11:26:02.261604 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>> [init tag: 3478239387] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>>> 2330749678]
>>>>>> 11:26:02.263583 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>> 11:26:02.264548 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>> 11:26:02.264652 IP 11.1.1.1.2905 > 120.1.1.1.2905: sctp (1) [HB REQ]
>>>>>> 11:26:02.264705 IP 120.1.1.1.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>> 11:26:02.563543 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>
>>>>>> From the above result, you can see that the INIT, COOKIE ECHO and
>>>>>> HB_REQ originated from 12.1.1.1 on eth1, but the ACK (INIT_ACK,
>>>>>> COOKIE_ACK, HB_ACK) are returned on eth2 using source address
>>>>>> 120.1.1.1 instead of 110.1.1.1.
>>>>>>
>>>>>> Why LKSCTP use 120.1.1.1 as source instead of 110.1.1.1?
>>>>>>
>>>>>> For simple ICMP ping test, it is normal, but not for SCTP.
>>>>>>
>>>>>> eth1
>>>>>> 11:30:02.824548 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>>>>>> seq 12, length 64
>>>>>> 11:30:02.824559 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>>>>>> seq 12, length 64
>>>>>> 11:30:03.825551 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>>>>>> seq 13, length 64
>>>>>> 11:30:03.825561 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>>>>>> seq 13, length 64
>>>>>>
>>>>>> eth2
>>>>>> 11:30:34.027687 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>>>>>> seq 2, length 64
>>>>>> 11:30:34.027697 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>>>>>> seq 2, length 64
>>>>>> 11:30:35.027686 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>>>>>> seq 3, length 64
>>>>>> 11:30:35.027694 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>>>>>> seq 3, length 64
>>>>>>
>>>>>> Below is the route information
>>>>>> #route -n
>>>>>> Kernel IP routing table
>>>>>> Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
>>>>>> 110.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth1
>>>>>> 120.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth2
>>>>>>
>>>>>> # ip route show
>>>>>> 110.1.1.0/24 dev eth1  proto kernel  scope link  src 110.1.1.1
>>>>>> 120.1.1.0/24 dev eth2  proto kernel  scope link  src 120.1.1.1
>>>>>>
>>>>>> Since we are using iproute2, so we will have dedicate routing table
>>>>>> per interface
>>>>>>
>>>>>> # ip route show table SCTP1
>>>>>> default via 110.1.1.254 dev eth1
>>>>>>
>>>>>> # ip route show table SCTP2
>>>>>> default via 120.1.1.254 dev eth2
>>>>>>
>>>>>> # ip rule ls
>>>>>> 0: from all lookup local
>>>>>> 101: from 110.1.1.1 lookup SCTP1
>>>>>> 102: from 120.1.1.1 lookup SCTP2
>>>>>> 32766: from all lookup main
>>>>>> 32767: from all lookup default
>>>>>>
>>>>>> How LKSCTP select source address to reply? If we know how it works,
>>>>>> then we may know what is going wrong.
>>>>>
>>>>> LKSCTP will prefer the address returned from the routing table as long
>>>>> as it is one of the addresses that is bound by the socket and are usable
>>>>> by the association.
>>>>>
>>>>> If the address returned from the route lookup is not part of the
>>>>> association, then lksctp attempts to lookup routes using one of the
>>>>> source addresses it has available.  Usually the first lookup succeeds
>>>>> due to the host-model implementation in linux.
>>>>>
>>>>> You may want to change your rule set to be destination based.  Then
>>>>> in the table associated with the rule, specify the source address
>>>>> you want to be used.
>>>>>
>>>>> -vlad
>>>>
>>>> I have had similar qualms myself about this behavior, and I honestly
>>>> don't know what the correct answer should be...
>>>>
>>>> In my opinion, shouldn't the source address "just work" for
>>>> acknowledgements? If the spec explicitly states that the ACK should
>>>> have a source address that matches the destination of the chunk being
>>>> ACKed, why should someone have to configure this behavior outside of
>>>> the SCTP stack by default? Is it a technical limitation, or is this
>>>> done for a particular reason?  I can understand needing to override
>>>> the behavior, but why isn't the default "sane"?
>>>
>>> I think the results are sane, they simply may not match expectations.
>>> SCTP spec doesn't say anything about source address selection.  It
>>> says that a response should be send back to the source of the request.
>>> This is being done in both cases, i.e. the destination address in
>>> INIT-ACK matches the source of the INIT.
>>>
>>> The spec does contain the MAY text that allows finer control of source
>>> addresses, but lksctp doesn't seem to implement that.  Whenever we've
>>> tried, we couldn't get the generic mechanism working to please everyone,
>>> as everyone had slightly different configurations and expectations.  So
>>> we left it to the rules engine.
>>>
>>> In this setup, it just appears that the default routing is not what you
>>> expect.  You can easily check this with 'ip route get' command.  If it
>>> is not what you want linux allows you to change that via ip rules.
>>>
>>> -vlad
>>>
>>>>
>>>> Karl
>>>>
>>>>>>
>>>>>> On Wed, Nov 27, 2013 at 8:45 PM, Neil Horman <nhorman@tuxdriver.com> wrote:
>>>>>>> On Wed, Nov 27, 2013 at 07:10:49AM +0800, Sun Paul wrote:
>>>>>>>> Hi Vlad
>>>>>>>>
>>>>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>>>>
>>>>>>> Because You only ever use one address from NODE A (12.1.1.1)
>>>>>>>
>>>>>>>> In the single-homing sample that provided in the original email, both
>>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>>>>> respond to the SCTP request.
>>>>>>>>
>>>>>>> Yes, because it does a route lookup to each of the two ip addresses to NODE B,
>>>>>>> and in both lookups, the route indicates that only one source address should be
>>>>>>> used (12.1.1.1).  If you issue a ip route show command, you'll see that routes
>>>>>>> to both address on NODE B match on a rule that specifies the same src address
>>>>>>> and interface be used.
>>>>>>>
>>>>>>> Neil
>>>>>>>
>>>>>>>> - PS
>>>>>>>>
>>>>>>>> On Wed, Nov 27, 2013 at 7:09 AM, Sun Paul <paulrbk@gmail.com> wrote:
>>>>>>>>> Hi Vlad
>>>>>>>>>
>>>>>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>>>>>
>>>>>>>>> In the single-homing sample that provided in the original email, both
>>>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>>>>>> respond to the SCTP request.
>>>>>>>>>
>>>>>>>>> - PS
>>>>>>>>>
>>>>>>>>> On Tue, Nov 26, 2013 at 11:19 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>>>>>>>> On 11/25/2013 08:03 PM, Sun Paul wrote:
>>>>>>>>>>> Hi
>>>>>>>>>>>
>>>>>>>>>>> we have a problem on using LKSCTP to form a 4 ways multi-homing network.
>>>>>>>>>>>
>>>>>>>>>>> Configuration
>>>>>>>>>>> - Node-A has 2 IP addresses in different subnets, known as IP-A (eth1),
>>>>>>>>>>> IP-B (eth2)
>>>>>>>>>>> - Node-B has 2 IP addresses in different subnets, known as IP-X (eth1),
>>>>>>>>>>> IP-Y (eth2)
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> First of all, this is not a 4 way multi-homed network.  As far as each
>>>>>>>>>> SCTP association is concerned, it has only 2 destinations to send to
>>>>>>>>>> so it has only 2 ways to get there.  The fact that you have multiple
>>>>>>>>>> local addresses doesn't mean that every local address can and should
>>>>>>>>>> be used to connect to the remote.
>>>>>>>>>>
>>>>>>>>>>> the four way paths are shown below.
>>>>>>>>>>> 1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>>>> 2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>>>> 3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>>>> 4. IP-B (12.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>>>
>>>>>>>>>> No, actually you only have 2 paths:  one to IPX and one to IP-Y.
>>>>>>>>>> Which source address you choose is based on routing policy
>>>>>>>>>> decisions and is outside the scope of SCTP.
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> the HB/HB_ACK is normal for the paths " IP-A to IP-X" and "IP-B to
>>>>>>>>>>> IP-Y", but it is not correct for the rest of two.
>>>>>>>>>>
>>>>>>>>>> Right, because linux is using a host addressing model, not an interface
>>>>>>>>>> addressing model.  SCTP stack simply finds the best source address
>>>>>>>>>> that can be used to reach IP-X and it happens to be IP-A.  So that
>>>>>>>>>> is what it is going to use.
>>>>>>>>>>
>>>>>>>>>> The above explains why you are seeing what you describe below.
>>>>>>>>>>
>>>>>>>>>> In the end, linux SCTP implementation determines paths solely based
>>>>>>>>>> on the destination address.
>>>>>>>>>>
>>>>>>>>>> -vlad
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> First of all, we are using iproute2 to form 2 table such that when
>>>>>>>>>>> IP-B arrives on IP-X, it will know how to route back to IP-B on the
>>>>>>>>>>> same interface, i.e (eth1). Same logic for the path "IP-A to IP-X".
>>>>>>>>>>>
>>>>>>>>>>> What we observed here is that when 12.1.1.1 sends INIT to 11.1.1.11,
>>>>>>>>>>> LKSCTP will send back the INIT_ACK to 12.1.1.1 using 12.1.1.11 but not
>>>>>>>>>>> using the IP 11.1.1.11.
>>>>>>>>>>>
>>>>>>>>>>> The above operation makes the subsequence HB/HB_ACK in using wrong IP address.
>>>>>>>>>>>
>>>>>>>>>>> TCP trace on eth1
>>>>>>>>>>> 18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>>>>>> [init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>>>>> 18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>>>>>> 18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>> 18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>> 18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>> 18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>> 18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>>
>>>>>>>>>>> TCP trace on eth2
>>>>>>>>>>> 18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>>>>> [init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>>>>>>>> 3340756356]
>>>>>>>>>>> 18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>>>>> 18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>> 18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>> 18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>> 18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>> 18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>> 18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>> 18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>> 18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> If we are using single homing, there is no problem on the SCTP
>>>>>>>>>>> communication. Below is the TCP trace on eth1 using sctp_test
>>>>>>>>>>>
>>>>>>>>>>> 18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>>>>>> [init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>>>>> 18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>>>>> [init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16] [init TSN:
>>>>>>>>>>> 1877695021]
>>>>>>>>>>> 18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>>>>>> 18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>>>>> 18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>> 18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>> 18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [DATA]
>>>>>>>>>>> (B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
>>>>>>>>>>> 18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [SACK]
>>>>>>>>>>> [cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
>>>>>>>>>>> 18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>> 18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>>
>>>>>>>>>>> From the observations, it seems that the LKSCTP library is not able to
>>>>>>>>>>> use the original local address when multi-homing is being used. Is
>>>>>>>>>>> there anyway can be resolved it?
>>>>>>>>>>>
>>>>>>>>>>> Thanks
>>>>>>>>>>>
>>>>>>>>>>> PS
>>>>>>>>>>> --
>>>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>> --
>>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>>>
>>>>>
>>>>> --
>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>> the body of a message to majordomo@vger.kernel.org
>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>
>

Re: Supporting 4 way connections in LKSCTP

[Vlad Yasevich]

On 12/02/2013 09:19 PM, Sun Paul wrote:
> so in this case, says
> 
> (NODE-A) IP-B send INIT to IP-X (NODE-B), and then IP-Y (NODE-B)
> returns INIT_ACK to IP-B (NODE-A)
> 
> this is also treated as a valid, am I correct?

As long as IP-X (Node-B) is present in the address list of the INIT-ACK
chunk, yes.

There is the code in __sctp_rcv_lookup_harder() that looks for other
adddresses in the INIT and INIT-ACK chunks.

-vlad
> 
> 
> On Tue, Dec 3, 2013 at 10:03 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>> On 12/02/2013 08:39 PM, Sun Paul wrote:
>>> Another question
>>>
>>> if a wrong source IP is used, does the association still classified as normal?
>>
>> What do you mean my wrong source IP?  As long as the address is part of
>> the association, it can be used.
>>
>> -vlad
>>
>>>
>>> On Tue, Dec 3, 2013 at 9:31 AM, Sun Paul <paulrbk@gmail.com> wrote:
>>>> Thanks Vlad
>>>>
>>>> I checked on the route, and it looks correct.
>>>>
>>>> [root@localhost ~]# ip route get 11.1.1.1 from 110.1.1.1
>>>> 11.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
>>>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>>>
>>>> [root@localhost ~]# ip route get 11.1.1.1 from 120.1.1.1
>>>> 11.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
>>>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>>>
>>>> [root@localhost ~]# ip route get 12.1.1.1 from 120.1.1.1
>>>> 12.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
>>>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>>>
>>>> [root@localhost ~]# ip route get 12.1.1.1 from 110.1.1.1
>>>> 12.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
>>>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>>>
>>>> so, if this is not being handled in LKSCTP, is it possible to suggest
>>>> a way how we can achieve it?
>>>>
>>>> On Tue, Dec 3, 2013 at 12:42 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>>> On 12/02/2013 10:45 AM, Karl Heiss wrote:
>>>>>> On Mon, Dec 2, 2013 at 9:38 AM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>>>>> On 11/27/2013 11:03 PM, Sun Paul wrote:
>>>>>>>> How LKSCTP select which source address to use for the INIT_ACK or
>>>>>>>> HB_ACK? below is the testing result where a router is located in the
>>>>>>>> middle.
>>>>>>>>
>>>>>>>> Before starting the application. the packet on eth1 and eth2 are
>>>>>>>>
>>>>>>>> eth1
>>>>>>>> 0 packets dropped by kernel
>>>>>>>> [root@localhost ~]# tcpdump -i eth1 -s 0 -nn
>>>>>>>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>>>>>>>> listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
>>>>>>>> 11:24:14.262489 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>>>> [init tag: 28362903] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>> 11:24:14.262522 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>>>>>>> 11:24:14.539486
>>>>>>>> 11:24:16.262488 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>>>> [init tag: 29391734] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>> 11:24:16.262520 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [ABORT]
>>>>>>>>
>>>>>>>> eth2
>>>>>>>> [root@localhost ~]# tcpdump -i eth2 -s 0 -nn
>>>>>>>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>>>>>>>> listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes
>>>>>>>>
>>>>>>>> When starting the application. the packet show as below.
>>>>>>>>
>>>>>>>> eth1
>>>>>>>> 11:26:02.261511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>>>> [init tag: 26256828] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>> 11:26:02.263513 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [COOKIE ECHO]
>>>>>>>> 11:26:02.264518 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>>>>>>> 11:26:02.563511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB REQ]
>>>>>>>>
>>>>>>>> eth2
>>>>>>>> 11:26:02.261604 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>> [init tag: 3478239387] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>>>>> 2330749678]
>>>>>>>> 11:26:02.263583 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>> 11:26:02.264548 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>> 11:26:02.264652 IP 11.1.1.1.2905 > 120.1.1.1.2905: sctp (1) [HB REQ]
>>>>>>>> 11:26:02.264705 IP 120.1.1.1.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>> 11:26:02.563543 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>
>>>>>>>> From the above result, you can see that the INIT, COOKIE ECHO and
>>>>>>>> HB_REQ originated from 12.1.1.1 on eth1, but the ACK (INIT_ACK,
>>>>>>>> COOKIE_ACK, HB_ACK) are returned on eth2 using source address
>>>>>>>> 120.1.1.1 instead of 110.1.1.1.
>>>>>>>>
>>>>>>>> Why LKSCTP use 120.1.1.1 as source instead of 110.1.1.1?
>>>>>>>>
>>>>>>>> For simple ICMP ping test, it is normal, but not for SCTP.
>>>>>>>>
>>>>>>>> eth1
>>>>>>>> 11:30:02.824548 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>>>>>>>> seq 12, length 64
>>>>>>>> 11:30:02.824559 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>>>>>>>> seq 12, length 64
>>>>>>>> 11:30:03.825551 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id 37178,
>>>>>>>> seq 13, length 64
>>>>>>>> 11:30:03.825561 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id 37178,
>>>>>>>> seq 13, length 64
>>>>>>>>
>>>>>>>> eth2
>>>>>>>> 11:30:34.027687 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>>>>>>>> seq 2, length 64
>>>>>>>> 11:30:34.027697 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>>>>>>>> seq 2, length 64
>>>>>>>> 11:30:35.027686 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id 46138,
>>>>>>>> seq 3, length 64
>>>>>>>> 11:30:35.027694 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id 46138,
>>>>>>>> seq 3, length 64
>>>>>>>>
>>>>>>>> Below is the route information
>>>>>>>> #route -n
>>>>>>>> Kernel IP routing table
>>>>>>>> Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
>>>>>>>> 110.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth1
>>>>>>>> 120.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 eth2
>>>>>>>>
>>>>>>>> # ip route show
>>>>>>>> 110.1.1.0/24 dev eth1  proto kernel  scope link  src 110.1.1.1
>>>>>>>> 120.1.1.0/24 dev eth2  proto kernel  scope link  src 120.1.1.1
>>>>>>>>
>>>>>>>> Since we are using iproute2, so we will have dedicate routing table
>>>>>>>> per interface
>>>>>>>>
>>>>>>>> # ip route show table SCTP1
>>>>>>>> default via 110.1.1.254 dev eth1
>>>>>>>>
>>>>>>>> # ip route show table SCTP2
>>>>>>>> default via 120.1.1.254 dev eth2
>>>>>>>>
>>>>>>>> # ip rule ls
>>>>>>>> 0: from all lookup local
>>>>>>>> 101: from 110.1.1.1 lookup SCTP1
>>>>>>>> 102: from 120.1.1.1 lookup SCTP2
>>>>>>>> 32766: from all lookup main
>>>>>>>> 32767: from all lookup default
>>>>>>>>
>>>>>>>> How LKSCTP select source address to reply? If we know how it works,
>>>>>>>> then we may know what is going wrong.
>>>>>>>
>>>>>>> LKSCTP will prefer the address returned from the routing table as long
>>>>>>> as it is one of the addresses that is bound by the socket and are usable
>>>>>>> by the association.
>>>>>>>
>>>>>>> If the address returned from the route lookup is not part of the
>>>>>>> association, then lksctp attempts to lookup routes using one of the
>>>>>>> source addresses it has available.  Usually the first lookup succeeds
>>>>>>> due to the host-model implementation in linux.
>>>>>>>
>>>>>>> You may want to change your rule set to be destination based.  Then
>>>>>>> in the table associated with the rule, specify the source address
>>>>>>> you want to be used.
>>>>>>>
>>>>>>> -vlad
>>>>>>
>>>>>> I have had similar qualms myself about this behavior, and I honestly
>>>>>> don't know what the correct answer should be...
>>>>>>
>>>>>> In my opinion, shouldn't the source address "just work" for
>>>>>> acknowledgements? If the spec explicitly states that the ACK should
>>>>>> have a source address that matches the destination of the chunk being
>>>>>> ACKed, why should someone have to configure this behavior outside of
>>>>>> the SCTP stack by default? Is it a technical limitation, or is this
>>>>>> done for a particular reason?  I can understand needing to override
>>>>>> the behavior, but why isn't the default "sane"?
>>>>>
>>>>> I think the results are sane, they simply may not match expectations.
>>>>> SCTP spec doesn't say anything about source address selection.  It
>>>>> says that a response should be send back to the source of the request.
>>>>> This is being done in both cases, i.e. the destination address in
>>>>> INIT-ACK matches the source of the INIT.
>>>>>
>>>>> The spec does contain the MAY text that allows finer control of source
>>>>> addresses, but lksctp doesn't seem to implement that.  Whenever we've
>>>>> tried, we couldn't get the generic mechanism working to please everyone,
>>>>> as everyone had slightly different configurations and expectations.  So
>>>>> we left it to the rules engine.
>>>>>
>>>>> In this setup, it just appears that the default routing is not what you
>>>>> expect.  You can easily check this with 'ip route get' command.  If it
>>>>> is not what you want linux allows you to change that via ip rules.
>>>>>
>>>>> -vlad
>>>>>
>>>>>>
>>>>>> Karl
>>>>>>
>>>>>>>>
>>>>>>>> On Wed, Nov 27, 2013 at 8:45 PM, Neil Horman <nhorman@tuxdriver.com> wrote:
>>>>>>>>> On Wed, Nov 27, 2013 at 07:10:49AM +0800, Sun Paul wrote:
>>>>>>>>>> Hi Vlad
>>>>>>>>>>
>>>>>>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>>>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>>>>>>
>>>>>>>>> Because You only ever use one address from NODE A (12.1.1.1)
>>>>>>>>>
>>>>>>>>>> In the single-homing sample that provided in the original email, both
>>>>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>>>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>>>>>>> respond to the SCTP request.
>>>>>>>>>>
>>>>>>>>> Yes, because it does a route lookup to each of the two ip addresses to NODE B,
>>>>>>>>> and in both lookups, the route indicates that only one source address should be
>>>>>>>>> used (12.1.1.1).  If you issue a ip route show command, you'll see that routes
>>>>>>>>> to both address on NODE B match on a rule that specifies the same src address
>>>>>>>>> and interface be used.
>>>>>>>>>
>>>>>>>>> Neil
>>>>>>>>>
>>>>>>>>>> - PS
>>>>>>>>>>
>>>>>>>>>> On Wed, Nov 27, 2013 at 7:09 AM, Sun Paul <paulrbk@gmail.com> wrote:
>>>>>>>>>>> Hi Vlad
>>>>>>>>>>>
>>>>>>>>>>> Thank for your reply. If it is based on the destination IP to find the
>>>>>>>>>>> best route, why the problem didn't happen on single-homing sample?
>>>>>>>>>>>
>>>>>>>>>>> In the single-homing sample that provided in the original email, both
>>>>>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B during the
>>>>>>>>>>> test. However, the LKSCTP library know to use the interface eth1 to
>>>>>>>>>>> respond to the SCTP request.
>>>>>>>>>>>
>>>>>>>>>>> - PS
>>>>>>>>>>>
>>>>>>>>>>> On Tue, Nov 26, 2013 at 11:19 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>>>>>>>>>> On 11/25/2013 08:03 PM, Sun Paul wrote:
>>>>>>>>>>>>> Hi
>>>>>>>>>>>>>
>>>>>>>>>>>>> we have a problem on using LKSCTP to form a 4 ways multi-homing network.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Configuration
>>>>>>>>>>>>> - Node-A has 2 IP addresses in different subnets, known as IP-A (eth1),
>>>>>>>>>>>>> IP-B (eth2)
>>>>>>>>>>>>> - Node-B has 2 IP addresses in different subnets, known as IP-X (eth1),
>>>>>>>>>>>>> IP-Y (eth2)
>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> First of all, this is not a 4 way multi-homed network.  As far as each
>>>>>>>>>>>> SCTP association is concerned, it has only 2 destinations to send to
>>>>>>>>>>>> so it has only 2 ways to get there.  The fact that you have multiple
>>>>>>>>>>>> local addresses doesn't mean that every local address can and should
>>>>>>>>>>>> be used to connect to the remote.
>>>>>>>>>>>>
>>>>>>>>>>>>> the four way paths are shown below.
>>>>>>>>>>>>> 1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>>>>>> 2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>>>>>> 3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>>>>>> 4. IP-B (12.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>>>>>
>>>>>>>>>>>> No, actually you only have 2 paths:  one to IPX and one to IP-Y.
>>>>>>>>>>>> Which source address you choose is based on routing policy
>>>>>>>>>>>> decisions and is outside the scope of SCTP.
>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> the HB/HB_ACK is normal for the paths " IP-A to IP-X" and "IP-B to
>>>>>>>>>>>>> IP-Y", but it is not correct for the rest of two.
>>>>>>>>>>>>
>>>>>>>>>>>> Right, because linux is using a host addressing model, not an interface
>>>>>>>>>>>> addressing model.  SCTP stack simply finds the best source address
>>>>>>>>>>>> that can be used to reach IP-X and it happens to be IP-A.  So that
>>>>>>>>>>>> is what it is going to use.
>>>>>>>>>>>>
>>>>>>>>>>>> The above explains why you are seeing what you describe below.
>>>>>>>>>>>>
>>>>>>>>>>>> In the end, linux SCTP implementation determines paths solely based
>>>>>>>>>>>> on the destination address.
>>>>>>>>>>>>
>>>>>>>>>>>> -vlad
>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> First of all, we are using iproute2 to form 2 table such that when
>>>>>>>>>>>>> IP-B arrives on IP-X, it will know how to route back to IP-B on the
>>>>>>>>>>>>> same interface, i.e (eth1). Same logic for the path "IP-A to IP-X".
>>>>>>>>>>>>>
>>>>>>>>>>>>> What we observed here is that when 12.1.1.1 sends INIT to 11.1.1.11,
>>>>>>>>>>>>> LKSCTP will send back the INIT_ACK to 12.1.1.1 using 12.1.1.11 but not
>>>>>>>>>>>>> using the IP 11.1.1.11.
>>>>>>>>>>>>>
>>>>>>>>>>>>> The above operation makes the subsequence HB/HB_ACK in using wrong IP address.
>>>>>>>>>>>>>
>>>>>>>>>>>>> TCP trace on eth1
>>>>>>>>>>>>> 18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>>>>>>>> [init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>>>>>>> 18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>>>>>>>> 18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>>> 18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>>>> 18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>>>> 18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>>>> 18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>>>>
>>>>>>>>>>>>> TCP trace on eth2
>>>>>>>>>>>>> 18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>>>>>>> [init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>>>>>>>>>> 3340756356]
>>>>>>>>>>>>> 18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>>>>>>> 18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>>>> 18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>>> 18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>>> 18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>>> 18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>>> 18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>>> 18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>>> 18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> If we are using single homing, there is no problem on the SCTP
>>>>>>>>>>>>> communication. Below is the TCP trace on eth1 using sctp_test
>>>>>>>>>>>>>
>>>>>>>>>>>>> 18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
>>>>>>>>>>>>> [init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
>>>>>>>>>>>>> 18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
>>>>>>>>>>>>> [init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16] [init TSN:
>>>>>>>>>>>>> 1877695021]
>>>>>>>>>>>>> 18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
>>>>>>>>>>>>> 18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
>>>>>>>>>>>>> 18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>>> 18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>>>> 18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [DATA]
>>>>>>>>>>>>> (B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
>>>>>>>>>>>>> 18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [SACK]
>>>>>>>>>>>>> [cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
>>>>>>>>>>>>> 18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
>>>>>>>>>>>>> 18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>>>>>>>>>>>>>
>>>>>>>>>>>>> From the observations, it seems that the LKSCTP library is not able to
>>>>>>>>>>>>> use the original local address when multi-homing is being used. Is
>>>>>>>>>>>>> there anyway can be resolved it?
>>>>>>>>>>>>>
>>>>>>>>>>>>> Thanks
>>>>>>>>>>>>>
>>>>>>>>>>>>> PS
>>>>>>>>>>>>> --
>>>>>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>> --
>>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>
>>

Re: Supporting 4 way connections in LKSCTP

[Vlad Yasevich]

On 12/03/2013 08:11 AM, Sun Paul wrote:
> But how about the HB and HB_ACK?  Still valid?

As long as the source address is part of the association, then yes
it is perfectly valid.

-vlad

> On Dec 3, 2013 8:32 PM, "Vlad Yasevich" <vyasevich@gmail.com> wrote:
> 
>> On 12/02/2013 09:19 PM, Sun Paul wrote:
>>> so in this case, says
>>>
>>> (NODE-A) IP-B send INIT to IP-X (NODE-B), and then IP-Y (NODE-B)
>>> returns INIT_ACK to IP-B (NODE-A)
>>>
>>> this is also treated as a valid, am I correct?
>>
>> As long as IP-X (Node-B) is present in the address list of the INIT-ACK
>> chunk, yes.
>>
>> There is the code in __sctp_rcv_lookup_harder() that looks for other
>> adddresses in the INIT and INIT-ACK chunks.
>>
>> -vlad
>>>
>>>
>>> On Tue, Dec 3, 2013 at 10:03 AM, Vlad Yasevich <vyasevich@gmail.com>
>> wrote:
>>>> On 12/02/2013 08:39 PM, Sun Paul wrote:
>>>>> Another question
>>>>>
>>>>> if a wrong source IP is used, does the association still classified as
>> normal?
>>>>
>>>> What do you mean my wrong source IP?  As long as the address is part of
>>>> the association, it can be used.
>>>>
>>>> -vlad
>>>>
>>>>>
>>>>> On Tue, Dec 3, 2013 at 9:31 AM, Sun Paul <paulrbk@gmail.com> wrote:
>>>>>> Thanks Vlad
>>>>>>
>>>>>> I checked on the route, and it looks correct.
>>>>>>
>>>>>> [root@localhost ~]# ip route get 11.1.1.1 from 110.1.1.1
>>>>>> 11.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
>>>>>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>>>>>
>>>>>> [root@localhost ~]# ip route get 11.1.1.1 from 120.1.1.1
>>>>>> 11.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
>>>>>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>>>>>
>>>>>> [root@localhost ~]# ip route get 12.1.1.1 from 120.1.1.1
>>>>>> 12.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
>>>>>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>>>>>
>>>>>> [root@localhost ~]# ip route get 12.1.1.1 from 110.1.1.1
>>>>>> 12.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
>>>>>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>>>>>
>>>>>> so, if this is not being handled in LKSCTP, is it possible to suggest
>>>>>> a way how we can achieve it?
>>>>>>
>>>>>> On Tue, Dec 3, 2013 at 12:42 AM, Vlad Yasevich <vyasevich@gmail.com>
>> wrote:
>>>>>>> On 12/02/2013 10:45 AM, Karl Heiss wrote:
>>>>>>>> On Mon, Dec 2, 2013 at 9:38 AM, Vlad Yasevich <vyasevich@gmail.com>
>> wrote:
>>>>>>>>> On 11/27/2013 11:03 PM, Sun Paul wrote:
>>>>>>>>>> How LKSCTP select which source address to use for the INIT_ACK or
>>>>>>>>>> HB_ACK? below is the testing result where a router is located in
>> the
>>>>>>>>>> middle.
>>>>>>>>>>
>>>>>>>>>> Before starting the application. the packet on eth1 and eth2 are
>>>>>>>>>>
>>>>>>>>>> eth1
>>>>>>>>>> 0 packets dropped by kernel
>>>>>>>>>> [root@localhost ~]# tcpdump -i eth1 -s 0 -nn
>>>>>>>>>> tcpdump: verbose output suppressed, use -v or -vv for full
>> protocol decode
>>>>>>>>>> listening on eth1, link-type EN10MB (Ethernet), capture size
>> 65535 bytes
>>>>>>>>>> 11:24:14.262489 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>>>>>> [init tag: 28362903] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN:
>> 0]
>>>>>>>>>> 11:24:14.262522 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1)
>> [ABORT]
>>>>>>>>>> 11:24:14.539486
>>>>>>>>>> 11:24:16.262488 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>>>>>> [init tag: 29391734] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN:
>> 0]
>>>>>>>>>> 11:24:16.262520 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1)
>> [ABORT]
>>>>>>>>>>
>>>>>>>>>> eth2
>>>>>>>>>> [root@localhost ~]# tcpdump -i eth2 -s 0 -nn
>>>>>>>>>> tcpdump: verbose output suppressed, use -v or -vv for full
>> protocol decode
>>>>>>>>>> listening on eth2, link-type EN10MB (Ethernet), capture size
>> 65535 bytes
>>>>>>>>>>
>>>>>>>>>> When starting the application. the packet show as below.
>>>>>>>>>>
>>>>>>>>>> eth1
>>>>>>>>>> 11:26:02.261511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>>>>>> [init tag: 26256828] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN:
>> 0]
>>>>>>>>>> 11:26:02.263513 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1)
>> [COOKIE ECHO]
>>>>>>>>>> 11:26:02.264518 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB
>> REQ]
>>>>>>>>>> 11:26:02.563511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB
>> REQ]
>>>>>>>>>>
>>>>>>>>>> eth2
>>>>>>>>>> 11:26:02.261604 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [INIT
>> ACK]
>>>>>>>>>> [init tag: 3478239387] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>>>>>>> 2330749678]
>>>>>>>>>> 11:26:02.263583 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1)
>> [COOKIE ACK]
>>>>>>>>>> 11:26:02.264548 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB
>> ACK]
>>>>>>>>>> 11:26:02.264652 IP 11.1.1.1.2905 > 120.1.1.1.2905: sctp (1) [HB
>> REQ]
>>>>>>>>>> 11:26:02.264705 IP 120.1.1.1.2905 > 11.1.1.1.2905: sctp (1) [HB
>> ACK]
>>>>>>>>>> 11:26:02.563543 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB
>> ACK]
>>>>>>>>>>
>>>>>>>>>> From the above result, you can see that the INIT, COOKIE ECHO and
>>>>>>>>>> HB_REQ originated from 12.1.1.1 on eth1, but the ACK (INIT_ACK,
>>>>>>>>>> COOKIE_ACK, HB_ACK) are returned on eth2 using source address
>>>>>>>>>> 120.1.1.1 instead of 110.1.1.1.
>>>>>>>>>>
>>>>>>>>>> Why LKSCTP use 120.1.1.1 as source instead of 110.1.1.1?
>>>>>>>>>>
>>>>>>>>>> For simple ICMP ping test, it is normal, but not for SCTP.
>>>>>>>>>>
>>>>>>>>>> eth1
>>>>>>>>>> 11:30:02.824548 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id
>> 37178,
>>>>>>>>>> seq 12, length 64
>>>>>>>>>> 11:30:02.824559 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id
>> 37178,
>>>>>>>>>> seq 12, length 64
>>>>>>>>>> 11:30:03.825551 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id
>> 37178,
>>>>>>>>>> seq 13, length 64
>>>>>>>>>> 11:30:03.825561 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id
>> 37178,
>>>>>>>>>> seq 13, length 64
>>>>>>>>>>
>>>>>>>>>> eth2
>>>>>>>>>> 11:30:34.027687 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id
>> 46138,
>>>>>>>>>> seq 2, length 64
>>>>>>>>>> 11:30:34.027697 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id
>> 46138,
>>>>>>>>>> seq 2, length 64
>>>>>>>>>> 11:30:35.027686 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id
>> 46138,
>>>>>>>>>> seq 3, length 64
>>>>>>>>>> 11:30:35.027694 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id
>> 46138,
>>>>>>>>>> seq 3, length 64
>>>>>>>>>>
>>>>>>>>>> Below is the route information
>>>>>>>>>> #route -n
>>>>>>>>>> Kernel IP routing table
>>>>>>>>>> Destination     Gateway         Genmask         Flags Metric Ref
>>    Use Iface
>>>>>>>>>> 110.1.1.0       0.0.0.0         255.255.255.0   U     0      0
>>      0 eth1
>>>>>>>>>> 120.1.1.0       0.0.0.0         255.255.255.0   U     0      0
>>      0 eth2
>>>>>>>>>>
>>>>>>>>>> # ip route show
>>>>>>>>>> 110.1.1.0/24 dev eth1  proto kernel  scope link  src 110.1.1.1
>>>>>>>>>> 120.1.1.0/24 dev eth2  proto kernel  scope link  src 120.1.1.1
>>>>>>>>>>
>>>>>>>>>> Since we are using iproute2, so we will have dedicate routing
>> table
>>>>>>>>>> per interface
>>>>>>>>>>
>>>>>>>>>> # ip route show table SCTP1
>>>>>>>>>> default via 110.1.1.254 dev eth1
>>>>>>>>>>
>>>>>>>>>> # ip route show table SCTP2
>>>>>>>>>> default via 120.1.1.254 dev eth2
>>>>>>>>>>
>>>>>>>>>> # ip rule ls
>>>>>>>>>> 0: from all lookup local
>>>>>>>>>> 101: from 110.1.1.1 lookup SCTP1
>>>>>>>>>> 102: from 120.1.1.1 lookup SCTP2
>>>>>>>>>> 32766: from all lookup main
>>>>>>>>>> 32767: from all lookup default
>>>>>>>>>>
>>>>>>>>>> How LKSCTP select source address to reply? If we know how it
>> works,
>>>>>>>>>> then we may know what is going wrong.
>>>>>>>>>
>>>>>>>>> LKSCTP will prefer the address returned from the routing table as
>> long
>>>>>>>>> as it is one of the addresses that is bound by the socket and are
>> usable
>>>>>>>>> by the association.
>>>>>>>>>
>>>>>>>>> If the address returned from the route lookup is not part of the
>>>>>>>>> association, then lksctp attempts to lookup routes using one of the
>>>>>>>>> source addresses it has available.  Usually the first lookup
>> succeeds
>>>>>>>>> due to the host-model implementation in linux.
>>>>>>>>>
>>>>>>>>> You may want to change your rule set to be destination based.  Then
>>>>>>>>> in the table associated with the rule, specify the source address
>>>>>>>>> you want to be used.
>>>>>>>>>
>>>>>>>>> -vlad
>>>>>>>>
>>>>>>>> I have had similar qualms myself about this behavior, and I honestly
>>>>>>>> don't know what the correct answer should be...
>>>>>>>>
>>>>>>>> In my opinion, shouldn't the source address "just work" for
>>>>>>>> acknowledgements? If the spec explicitly states that the ACK should
>>>>>>>> have a source address that matches the destination of the chunk
>> being
>>>>>>>> ACKed, why should someone have to configure this behavior outside of
>>>>>>>> the SCTP stack by default? Is it a technical limitation, or is this
>>>>>>>> done for a particular reason?  I can understand needing to override
>>>>>>>> the behavior, but why isn't the default "sane"?
>>>>>>>
>>>>>>> I think the results are sane, they simply may not match expectations.
>>>>>>> SCTP spec doesn't say anything about source address selection.  It
>>>>>>> says that a response should be send back to the source of the
>> request.
>>>>>>> This is being done in both cases, i.e. the destination address in
>>>>>>> INIT-ACK matches the source of the INIT.
>>>>>>>
>>>>>>> The spec does contain the MAY text that allows finer control of
>> source
>>>>>>> addresses, but lksctp doesn't seem to implement that.  Whenever we've
>>>>>>> tried, we couldn't get the generic mechanism working to please
>> everyone,
>>>>>>> as everyone had slightly different configurations and expectations.
>>  So
>>>>>>> we left it to the rules engine.
>>>>>>>
>>>>>>> In this setup, it just appears that the default routing is not what
>> you
>>>>>>> expect.  You can easily check this with 'ip route get' command.  If
>> it
>>>>>>> is not what you want linux allows you to change that via ip rules.
>>>>>>>
>>>>>>> -vlad
>>>>>>>
>>>>>>>>
>>>>>>>> Karl
>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On Wed, Nov 27, 2013 at 8:45 PM, Neil Horman <
>> nhorman@tuxdriver.com> wrote:
>>>>>>>>>>> On Wed, Nov 27, 2013 at 07:10:49AM +0800, Sun Paul wrote:
>>>>>>>>>>>> Hi Vlad
>>>>>>>>>>>>
>>>>>>>>>>>> Thank for your reply. If it is based on the destination IP to
>> find the
>>>>>>>>>>>> best route, why the problem didn't happen on single-homing
>> sample?
>>>>>>>>>>>>
>>>>>>>>>>> Because You only ever use one address from NODE A (12.1.1.1)
>>>>>>>>>>>
>>>>>>>>>>>> In the single-homing sample that provided in the original
>> email, both
>>>>>>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B
>> during the
>>>>>>>>>>>> test. However, the LKSCTP library know to use the interface
>> eth1 to
>>>>>>>>>>>> respond to the SCTP request.
>>>>>>>>>>>>
>>>>>>>>>>> Yes, because it does a route lookup to each of the two ip
>> addresses to NODE B,
>>>>>>>>>>> and in both lookups, the route indicates that only one source
>> address should be
>>>>>>>>>>> used (12.1.1.1).  If you issue a ip route show command, you'll
>> see that routes
>>>>>>>>>>> to both address on NODE B match on a rule that specifies the
>> same src address
>>>>>>>>>>> and interface be used.
>>>>>>>>>>>
>>>>>>>>>>> Neil
>>>>>>>>>>>
>>>>>>>>>>>> - PS
>>>>>>>>>>>>
>>>>>>>>>>>> On Wed, Nov 27, 2013 at 7:09 AM, Sun Paul <paulrbk@gmail.com>
>> wrote:
>>>>>>>>>>>>> Hi Vlad
>>>>>>>>>>>>>
>>>>>>>>>>>>> Thank for your reply. If it is based on the destination IP to
>> find the
>>>>>>>>>>>>> best route, why the problem didn't happen on single-homing
>> sample?
>>>>>>>>>>>>>
>>>>>>>>>>>>> In the single-homing sample that provided in the original
>> email, both
>>>>>>>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B
>> during the
>>>>>>>>>>>>> test. However, the LKSCTP library know to use the interface
>> eth1 to
>>>>>>>>>>>>> respond to the SCTP request.
>>>>>>>>>>>>>
>>>>>>>>>>>>> - PS
>>>>>>>>>>>>>
>>>>>>>>>>>>> On Tue, Nov 26, 2013 at 11:19 PM, Vlad Yasevich <
>> vyasevich@gmail.com> wrote:
>>>>>>>>>>>>>> On 11/25/2013 08:03 PM, Sun Paul wrote:
>>>>>>>>>>>>>>> Hi
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> we have a problem on using LKSCTP to form a 4 ways
>> multi-homing network.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Configuration
>>>>>>>>>>>>>>> - Node-A has 2 IP addresses in different subnets, known as
>> IP-A (eth1),
>>>>>>>>>>>>>>> IP-B (eth2)
>>>>>>>>>>>>>>> - Node-B has 2 IP addresses in different subnets, known as
>> IP-X (eth1),
>>>>>>>>>>>>>>> IP-Y (eth2)
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> First of all, this is not a 4 way multi-homed network.  As
>> far as each
>>>>>>>>>>>>>> SCTP association is concerned, it has only 2 destinations to
>> send to
>>>>>>>>>>>>>> so it has only 2 ways to get there.  The fact that you have
>> multiple
>>>>>>>>>>>>>> local addresses doesn't mean that every local address can and
>> should
>>>>>>>>>>>>>> be used to connect to the remote.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> the four way paths are shown below.
>>>>>>>>>>>>>>> 1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>>>>>>>> 2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>>>>>>>> 3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>>>>>>>> 4. IP-B (12.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> No, actually you only have 2 paths:  one to IPX and one to
>> IP-Y.
>>>>>>>>>>>>>> Which source address you choose is based on routing policy
>>>>>>>>>>>>>> decisions and is outside the scope of SCTP.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> the HB/HB_ACK is normal for the paths " IP-A to IP-X" and
>> "IP-B to
>>>>>>>>>>>>>>> IP-Y", but it is not correct for the rest of two.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Right, because linux is using a host addressing model, not an
>> interface
>>>>>>>>>>>>>> addressing model.  SCTP stack simply finds the best source
>> address
>>>>>>>>>>>>>> that can be used to reach IP-X and it happens to be IP-A.  So
>> that
>>>>>>>>>>>>>> is what it is going to use.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> The above explains why you are seeing what you describe below.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> In the end, linux SCTP implementation determines paths solely
>> based
>>>>>>>>>>>>>> on the destination address.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> -vlad
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> First of all, we are using iproute2 to form 2 table such
>> that when
>>>>>>>>>>>>>>> IP-B arrives on IP-X, it will know how to route back to IP-B
>> on the
>>>>>>>>>>>>>>> same interface, i.e (eth1). Same logic for the path "IP-A to
>> IP-X".
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> What we observed here is that when 12.1.1.1 sends INIT to
>> 11.1.1.11,
>>>>>>>>>>>>>>> LKSCTP will send back the INIT_ACK to 12.1.1.1 using
>> 12.1.1.11 but not
>>>>>>>>>>>>>>> using the IP 11.1.1.11.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> The above operation makes the subsequence HB/HB_ACK in using
>> wrong IP address.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> TCP trace on eth1
>>>>>>>>>>>>>>> 18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>> [INIT]
>>>>>>>>>>>>>>> [init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init
>> TSN: 0]
>>>>>>>>>>>>>>> 18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>> [COOKIE ECHO]
>>>>>>>>>>>>>>> 18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>> [HB REQ]
>>>>>>>>>>>>>>> 18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1)
>> [HB ACK]
>>>>>>>>>>>>>>> 18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1)
>> [HB ACK]
>>>>>>>>>>>>>>> 18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1)
>> [HB ACK]
>>>>>>>>>>>>>>> 18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1)
>> [HB ACK]
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> TCP trace on eth2
>>>>>>>>>>>>>>> 18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>> [INIT ACK]
>>>>>>>>>>>>>>> [init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init
>> TSN:
>>>>>>>>>>>>>>> 3340756356]
>>>>>>>>>>>>>>> 18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>> [COOKIE ACK]
>>>>>>>>>>>>>>> 18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>> [HB ACK]
>>>>>>>>>>>>>>> 18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>> [HB REQ]
>>>>>>>>>>>>>>> 18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>> [HB REQ]
>>>>>>>>>>>>>>> 18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>> [HB REQ]
>>>>>>>>>>>>>>> 18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>> [HB REQ]
>>>>>>>>>>>>>>> 18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>> [HB REQ]
>>>>>>>>>>>>>>> 18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>> [HB REQ]
>>>>>>>>>>>>>>> 18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>> [HB REQ]
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> If we are using single homing, there is no problem on the
>> SCTP
>>>>>>>>>>>>>>> communication. Below is the TCP trace on eth1 using sctp_test
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> 18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>> [INIT]
>>>>>>>>>>>>>>> [init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init
>> TSN: 0]
>>>>>>>>>>>>>>> 18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>> [INIT ACK]
>>>>>>>>>>>>>>> [init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16]
>> [init TSN:
>>>>>>>>>>>>>>> 1877695021]
>>>>>>>>>>>>>>> 18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>> [COOKIE ECHO]
>>>>>>>>>>>>>>> 18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>> [COOKIE ACK]
>>>>>>>>>>>>>>> 18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>> [HB REQ]
>>>>>>>>>>>>>>> 18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>> [HB ACK]
>>>>>>>>>>>>>>> 18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>> [DATA]
>>>>>>>>>>>>>>> (B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
>>>>>>>>>>>>>>> 18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>> [SACK]
>>>>>>>>>>>>>>> [cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
>>>>>>>>>>>>>>> 18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>> [HB REQ]
>>>>>>>>>>>>>>> 18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>> [HB ACK]
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> From the observations, it seems that the LKSCTP library is
>> not able to
>>>>>>>>>>>>>>> use the original local address when multi-homing is being
>> used. Is
>>>>>>>>>>>>>>> there anyway can be resolved it?
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Thanks
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> PS
>>>>>>>>>>>>>>> --
>>>>>>>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe
>> linux-sctp" in
>>>>>>>>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>>>>>>>>> More majordomo info at
>> http://vger.kernel.org/majordomo-info.html
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>> --
>>>>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe
>> linux-sctp" in
>>>>>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>>>>>> More majordomo info at
>> http://vger.kernel.org/majordomo-info.html
>>>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> --
>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe
>> linux-sctp" in
>>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>>
>>>>
>>
>>
> 

Re: Supporting 4 way connections in LKSCTP

[Sun Paul]

This is the most puzzling area. I really not sure whether it is really
valid or not. Is there any documented statement supporting this?

Let me summarize the behavior again.

NODE-A
eth1: IP-A
eth2: IP-B

NODE-B
eth1: IP-X
eth2: IP-Y

In normal operation, IP-A sends INIT to IP-X, IP-X returns INIT_ACK to
IP-A. IP-A then sends HB to IP-X, IP-X then returns HB_ACK to IP-A. In
the meantime, IP-B sends HB to IP-Y and IPY returns HB_ACK.

In case of the path between IP-A and IP-X is broken, IP-B sends INIT
to IP-X, NODE-B uses IP-Y to return INIT_ACK to IP-B. Then IP-B sends
HB to IP-X, and IP-Y returns HB_ACK to IP-B. In the meantime, the HB
communication between IP-B and IP-Y follows the normal flow.

Can I confirm, is it really valid?

On Tue, Dec 3, 2013 at 11:22 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
> On 12/03/2013 08:11 AM, Sun Paul wrote:
>> But how about the HB and HB_ACK?  Still valid?
>
> As long as the source address is part of the association, then yes
> it is perfectly valid.
>
> -vlad
>
>> On Dec 3, 2013 8:32 PM, "Vlad Yasevich" <vyasevich@gmail.com> wrote:
>>
>>> On 12/02/2013 09:19 PM, Sun Paul wrote:
>>>> so in this case, says
>>>>
>>>> (NODE-A) IP-B send INIT to IP-X (NODE-B), and then IP-Y (NODE-B)
>>>> returns INIT_ACK to IP-B (NODE-A)
>>>>
>>>> this is also treated as a valid, am I correct?
>>>
>>> As long as IP-X (Node-B) is present in the address list of the INIT-ACK
>>> chunk, yes.
>>>
>>> There is the code in __sctp_rcv_lookup_harder() that looks for other
>>> adddresses in the INIT and INIT-ACK chunks.
>>>
>>> -vlad
>>>>
>>>>
>>>> On Tue, Dec 3, 2013 at 10:03 AM, Vlad Yasevich <vyasevich@gmail.com>
>>> wrote:
>>>>> On 12/02/2013 08:39 PM, Sun Paul wrote:
>>>>>> Another question
>>>>>>
>>>>>> if a wrong source IP is used, does the association still classified as
>>> normal?
>>>>>
>>>>> What do you mean my wrong source IP?  As long as the address is part of
>>>>> the association, it can be used.
>>>>>
>>>>> -vlad
>>>>>
>>>>>>
>>>>>> On Tue, Dec 3, 2013 at 9:31 AM, Sun Paul <paulrbk@gmail.com> wrote:
>>>>>>> Thanks Vlad
>>>>>>>
>>>>>>> I checked on the route, and it looks correct.
>>>>>>>
>>>>>>> [root@localhost ~]# ip route get 11.1.1.1 from 110.1.1.1
>>>>>>> 11.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
>>>>>>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>>>>>>
>>>>>>> [root@localhost ~]# ip route get 11.1.1.1 from 120.1.1.1
>>>>>>> 11.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
>>>>>>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>>>>>>
>>>>>>> [root@localhost ~]# ip route get 12.1.1.1 from 120.1.1.1
>>>>>>> 12.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
>>>>>>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>>>>>>
>>>>>>> [root@localhost ~]# ip route get 12.1.1.1 from 110.1.1.1
>>>>>>> 12.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
>>>>>>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>>>>>>
>>>>>>> so, if this is not being handled in LKSCTP, is it possible to suggest
>>>>>>> a way how we can achieve it?
>>>>>>>
>>>>>>> On Tue, Dec 3, 2013 at 12:42 AM, Vlad Yasevich <vyasevich@gmail.com>
>>> wrote:
>>>>>>>> On 12/02/2013 10:45 AM, Karl Heiss wrote:
>>>>>>>>> On Mon, Dec 2, 2013 at 9:38 AM, Vlad Yasevich <vyasevich@gmail.com>
>>> wrote:
>>>>>>>>>> On 11/27/2013 11:03 PM, Sun Paul wrote:
>>>>>>>>>>> How LKSCTP select which source address to use for the INIT_ACK or
>>>>>>>>>>> HB_ACK? below is the testing result where a router is located in
>>> the
>>>>>>>>>>> middle.
>>>>>>>>>>>
>>>>>>>>>>> Before starting the application. the packet on eth1 and eth2 are
>>>>>>>>>>>
>>>>>>>>>>> eth1
>>>>>>>>>>> 0 packets dropped by kernel
>>>>>>>>>>> [root@localhost ~]# tcpdump -i eth1 -s 0 -nn
>>>>>>>>>>> tcpdump: verbose output suppressed, use -v or -vv for full
>>> protocol decode
>>>>>>>>>>> listening on eth1, link-type EN10MB (Ethernet), capture size
>>> 65535 bytes
>>>>>>>>>>> 11:24:14.262489 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>>>>>>> [init tag: 28362903] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN:
>>> 0]
>>>>>>>>>>> 11:24:14.262522 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1)
>>> [ABORT]
>>>>>>>>>>> 11:24:14.539486
>>>>>>>>>>> 11:24:16.262488 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>>>>>>> [init tag: 29391734] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN:
>>> 0]
>>>>>>>>>>> 11:24:16.262520 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1)
>>> [ABORT]
>>>>>>>>>>>
>>>>>>>>>>> eth2
>>>>>>>>>>> [root@localhost ~]# tcpdump -i eth2 -s 0 -nn
>>>>>>>>>>> tcpdump: verbose output suppressed, use -v or -vv for full
>>> protocol decode
>>>>>>>>>>> listening on eth2, link-type EN10MB (Ethernet), capture size
>>> 65535 bytes
>>>>>>>>>>>
>>>>>>>>>>> When starting the application. the packet show as below.
>>>>>>>>>>>
>>>>>>>>>>> eth1
>>>>>>>>>>> 11:26:02.261511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>>>>>>> [init tag: 26256828] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN:
>>> 0]
>>>>>>>>>>> 11:26:02.263513 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1)
>>> [COOKIE ECHO]
>>>>>>>>>>> 11:26:02.264518 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB
>>> REQ]
>>>>>>>>>>> 11:26:02.563511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB
>>> REQ]
>>>>>>>>>>>
>>>>>>>>>>> eth2
>>>>>>>>>>> 11:26:02.261604 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [INIT
>>> ACK]
>>>>>>>>>>> [init tag: 3478239387] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>>>>>>>> 2330749678]
>>>>>>>>>>> 11:26:02.263583 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1)
>>> [COOKIE ACK]
>>>>>>>>>>> 11:26:02.264548 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB
>>> ACK]
>>>>>>>>>>> 11:26:02.264652 IP 11.1.1.1.2905 > 120.1.1.1.2905: sctp (1) [HB
>>> REQ]
>>>>>>>>>>> 11:26:02.264705 IP 120.1.1.1.2905 > 11.1.1.1.2905: sctp (1) [HB
>>> ACK]
>>>>>>>>>>> 11:26:02.563543 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB
>>> ACK]
>>>>>>>>>>>
>>>>>>>>>>> From the above result, you can see that the INIT, COOKIE ECHO and
>>>>>>>>>>> HB_REQ originated from 12.1.1.1 on eth1, but the ACK (INIT_ACK,
>>>>>>>>>>> COOKIE_ACK, HB_ACK) are returned on eth2 using source address
>>>>>>>>>>> 120.1.1.1 instead of 110.1.1.1.
>>>>>>>>>>>
>>>>>>>>>>> Why LKSCTP use 120.1.1.1 as source instead of 110.1.1.1?
>>>>>>>>>>>
>>>>>>>>>>> For simple ICMP ping test, it is normal, but not for SCTP.
>>>>>>>>>>>
>>>>>>>>>>> eth1
>>>>>>>>>>> 11:30:02.824548 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id
>>> 37178,
>>>>>>>>>>> seq 12, length 64
>>>>>>>>>>> 11:30:02.824559 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id
>>> 37178,
>>>>>>>>>>> seq 12, length 64
>>>>>>>>>>> 11:30:03.825551 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id
>>> 37178,
>>>>>>>>>>> seq 13, length 64
>>>>>>>>>>> 11:30:03.825561 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id
>>> 37178,
>>>>>>>>>>> seq 13, length 64
>>>>>>>>>>>
>>>>>>>>>>> eth2
>>>>>>>>>>> 11:30:34.027687 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id
>>> 46138,
>>>>>>>>>>> seq 2, length 64
>>>>>>>>>>> 11:30:34.027697 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id
>>> 46138,
>>>>>>>>>>> seq 2, length 64
>>>>>>>>>>> 11:30:35.027686 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id
>>> 46138,
>>>>>>>>>>> seq 3, length 64
>>>>>>>>>>> 11:30:35.027694 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id
>>> 46138,
>>>>>>>>>>> seq 3, length 64
>>>>>>>>>>>
>>>>>>>>>>> Below is the route information
>>>>>>>>>>> #route -n
>>>>>>>>>>> Kernel IP routing table
>>>>>>>>>>> Destination     Gateway         Genmask         Flags Metric Ref
>>>    Use Iface
>>>>>>>>>>> 110.1.1.0       0.0.0.0         255.255.255.0   U     0      0
>>>      0 eth1
>>>>>>>>>>> 120.1.1.0       0.0.0.0         255.255.255.0   U     0      0
>>>      0 eth2
>>>>>>>>>>>
>>>>>>>>>>> # ip route show
>>>>>>>>>>> 110.1.1.0/24 dev eth1  proto kernel  scope link  src 110.1.1.1
>>>>>>>>>>> 120.1.1.0/24 dev eth2  proto kernel  scope link  src 120.1.1.1
>>>>>>>>>>>
>>>>>>>>>>> Since we are using iproute2, so we will have dedicate routing
>>> table
>>>>>>>>>>> per interface
>>>>>>>>>>>
>>>>>>>>>>> # ip route show table SCTP1
>>>>>>>>>>> default via 110.1.1.254 dev eth1
>>>>>>>>>>>
>>>>>>>>>>> # ip route show table SCTP2
>>>>>>>>>>> default via 120.1.1.254 dev eth2
>>>>>>>>>>>
>>>>>>>>>>> # ip rule ls
>>>>>>>>>>> 0: from all lookup local
>>>>>>>>>>> 101: from 110.1.1.1 lookup SCTP1
>>>>>>>>>>> 102: from 120.1.1.1 lookup SCTP2
>>>>>>>>>>> 32766: from all lookup main
>>>>>>>>>>> 32767: from all lookup default
>>>>>>>>>>>
>>>>>>>>>>> How LKSCTP select source address to reply? If we know how it
>>> works,
>>>>>>>>>>> then we may know what is going wrong.
>>>>>>>>>>
>>>>>>>>>> LKSCTP will prefer the address returned from the routing table as
>>> long
>>>>>>>>>> as it is one of the addresses that is bound by the socket and are
>>> usable
>>>>>>>>>> by the association.
>>>>>>>>>>
>>>>>>>>>> If the address returned from the route lookup is not part of the
>>>>>>>>>> association, then lksctp attempts to lookup routes using one of the
>>>>>>>>>> source addresses it has available.  Usually the first lookup
>>> succeeds
>>>>>>>>>> due to the host-model implementation in linux.
>>>>>>>>>>
>>>>>>>>>> You may want to change your rule set to be destination based.  Then
>>>>>>>>>> in the table associated with the rule, specify the source address
>>>>>>>>>> you want to be used.
>>>>>>>>>>
>>>>>>>>>> -vlad
>>>>>>>>>
>>>>>>>>> I have had similar qualms myself about this behavior, and I honestly
>>>>>>>>> don't know what the correct answer should be...
>>>>>>>>>
>>>>>>>>> In my opinion, shouldn't the source address "just work" for
>>>>>>>>> acknowledgements? If the spec explicitly states that the ACK should
>>>>>>>>> have a source address that matches the destination of the chunk
>>> being
>>>>>>>>> ACKed, why should someone have to configure this behavior outside of
>>>>>>>>> the SCTP stack by default? Is it a technical limitation, or is this
>>>>>>>>> done for a particular reason?  I can understand needing to override
>>>>>>>>> the behavior, but why isn't the default "sane"?
>>>>>>>>
>>>>>>>> I think the results are sane, they simply may not match expectations.
>>>>>>>> SCTP spec doesn't say anything about source address selection.  It
>>>>>>>> says that a response should be send back to the source of the
>>> request.
>>>>>>>> This is being done in both cases, i.e. the destination address in
>>>>>>>> INIT-ACK matches the source of the INIT.
>>>>>>>>
>>>>>>>> The spec does contain the MAY text that allows finer control of
>>> source
>>>>>>>> addresses, but lksctp doesn't seem to implement that.  Whenever we've
>>>>>>>> tried, we couldn't get the generic mechanism working to please
>>> everyone,
>>>>>>>> as everyone had slightly different configurations and expectations.
>>>  So
>>>>>>>> we left it to the rules engine.
>>>>>>>>
>>>>>>>> In this setup, it just appears that the default routing is not what
>>> you
>>>>>>>> expect.  You can easily check this with 'ip route get' command.  If
>>> it
>>>>>>>> is not what you want linux allows you to change that via ip rules.
>>>>>>>>
>>>>>>>> -vlad
>>>>>>>>
>>>>>>>>>
>>>>>>>>> Karl
>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> On Wed, Nov 27, 2013 at 8:45 PM, Neil Horman <
>>> nhorman@tuxdriver.com> wrote:
>>>>>>>>>>>> On Wed, Nov 27, 2013 at 07:10:49AM +0800, Sun Paul wrote:
>>>>>>>>>>>>> Hi Vlad
>>>>>>>>>>>>>
>>>>>>>>>>>>> Thank for your reply. If it is based on the destination IP to
>>> find the
>>>>>>>>>>>>> best route, why the problem didn't happen on single-homing
>>> sample?
>>>>>>>>>>>>>
>>>>>>>>>>>> Because You only ever use one address from NODE A (12.1.1.1)
>>>>>>>>>>>>
>>>>>>>>>>>>> In the single-homing sample that provided in the original
>>> email, both
>>>>>>>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B
>>> during the
>>>>>>>>>>>>> test. However, the LKSCTP library know to use the interface
>>> eth1 to
>>>>>>>>>>>>> respond to the SCTP request.
>>>>>>>>>>>>>
>>>>>>>>>>>> Yes, because it does a route lookup to each of the two ip
>>> addresses to NODE B,
>>>>>>>>>>>> and in both lookups, the route indicates that only one source
>>> address should be
>>>>>>>>>>>> used (12.1.1.1).  If you issue a ip route show command, you'll
>>> see that routes
>>>>>>>>>>>> to both address on NODE B match on a rule that specifies the
>>> same src address
>>>>>>>>>>>> and interface be used.
>>>>>>>>>>>>
>>>>>>>>>>>> Neil
>>>>>>>>>>>>
>>>>>>>>>>>>> - PS
>>>>>>>>>>>>>
>>>>>>>>>>>>> On Wed, Nov 27, 2013 at 7:09 AM, Sun Paul <paulrbk@gmail.com>
>>> wrote:
>>>>>>>>>>>>>> Hi Vlad
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Thank for your reply. If it is based on the destination IP to
>>> find the
>>>>>>>>>>>>>> best route, why the problem didn't happen on single-homing
>>> sample?
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> In the single-homing sample that provided in the original
>>> email, both
>>>>>>>>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B
>>> during the
>>>>>>>>>>>>>> test. However, the LKSCTP library know to use the interface
>>> eth1 to
>>>>>>>>>>>>>> respond to the SCTP request.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> - PS
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> On Tue, Nov 26, 2013 at 11:19 PM, Vlad Yasevich <
>>> vyasevich@gmail.com> wrote:
>>>>>>>>>>>>>>> On 11/25/2013 08:03 PM, Sun Paul wrote:
>>>>>>>>>>>>>>>> Hi
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> we have a problem on using LKSCTP to form a 4 ways
>>> multi-homing network.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> Configuration
>>>>>>>>>>>>>>>> - Node-A has 2 IP addresses in different subnets, known as
>>> IP-A (eth1),
>>>>>>>>>>>>>>>> IP-B (eth2)
>>>>>>>>>>>>>>>> - Node-B has 2 IP addresses in different subnets, known as
>>> IP-X (eth1),
>>>>>>>>>>>>>>>> IP-Y (eth2)
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> First of all, this is not a 4 way multi-homed network.  As
>>> far as each
>>>>>>>>>>>>>>> SCTP association is concerned, it has only 2 destinations to
>>> send to
>>>>>>>>>>>>>>> so it has only 2 ways to get there.  The fact that you have
>>> multiple
>>>>>>>>>>>>>>> local addresses doesn't mean that every local address can and
>>> should
>>>>>>>>>>>>>>> be used to connect to the remote.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> the four way paths are shown below.
>>>>>>>>>>>>>>>> 1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>>>>>>>>> 2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>>>>>>>>> 3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>>>>>>>>> 4. IP-B (12.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> No, actually you only have 2 paths:  one to IPX and one to
>>> IP-Y.
>>>>>>>>>>>>>>> Which source address you choose is based on routing policy
>>>>>>>>>>>>>>> decisions and is outside the scope of SCTP.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> the HB/HB_ACK is normal for the paths " IP-A to IP-X" and
>>> "IP-B to
>>>>>>>>>>>>>>>> IP-Y", but it is not correct for the rest of two.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Right, because linux is using a host addressing model, not an
>>> interface
>>>>>>>>>>>>>>> addressing model.  SCTP stack simply finds the best source
>>> address
>>>>>>>>>>>>>>> that can be used to reach IP-X and it happens to be IP-A.  So
>>> that
>>>>>>>>>>>>>>> is what it is going to use.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> The above explains why you are seeing what you describe below.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> In the end, linux SCTP implementation determines paths solely
>>> based
>>>>>>>>>>>>>>> on the destination address.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> -vlad
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> First of all, we are using iproute2 to form 2 table such
>>> that when
>>>>>>>>>>>>>>>> IP-B arrives on IP-X, it will know how to route back to IP-B
>>> on the
>>>>>>>>>>>>>>>> same interface, i.e (eth1). Same logic for the path "IP-A to
>>> IP-X".
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> What we observed here is that when 12.1.1.1 sends INIT to
>>> 11.1.1.11,
>>>>>>>>>>>>>>>> LKSCTP will send back the INIT_ACK to 12.1.1.1 using
>>> 12.1.1.11 but not
>>>>>>>>>>>>>>>> using the IP 11.1.1.11.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> The above operation makes the subsequence HB/HB_ACK in using
>>> wrong IP address.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> TCP trace on eth1
>>>>>>>>>>>>>>>> 18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>>> [INIT]
>>>>>>>>>>>>>>>> [init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init
>>> TSN: 0]
>>>>>>>>>>>>>>>> 18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>>> [COOKIE ECHO]
>>>>>>>>>>>>>>>> 18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>>> [HB REQ]
>>>>>>>>>>>>>>>> 18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1)
>>> [HB ACK]
>>>>>>>>>>>>>>>> 18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1)
>>> [HB ACK]
>>>>>>>>>>>>>>>> 18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1)
>>> [HB ACK]
>>>>>>>>>>>>>>>> 18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1)
>>> [HB ACK]
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> TCP trace on eth2
>>>>>>>>>>>>>>>> 18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>>> [INIT ACK]
>>>>>>>>>>>>>>>> [init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init
>>> TSN:
>>>>>>>>>>>>>>>> 3340756356]
>>>>>>>>>>>>>>>> 18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>>> [COOKIE ACK]
>>>>>>>>>>>>>>>> 18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>>> [HB ACK]
>>>>>>>>>>>>>>>> 18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>>> [HB REQ]
>>>>>>>>>>>>>>>> 18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>>> [HB REQ]
>>>>>>>>>>>>>>>> 18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>>> [HB REQ]
>>>>>>>>>>>>>>>> 18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>>> [HB REQ]
>>>>>>>>>>>>>>>> 18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>>> [HB REQ]
>>>>>>>>>>>>>>>> 18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>>> [HB REQ]
>>>>>>>>>>>>>>>> 18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>>> [HB REQ]
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> If we are using single homing, there is no problem on the
>>> SCTP
>>>>>>>>>>>>>>>> communication. Below is the TCP trace on eth1 using sctp_test
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> 18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>>> [INIT]
>>>>>>>>>>>>>>>> [init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init
>>> TSN: 0]
>>>>>>>>>>>>>>>> 18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>>> [INIT ACK]
>>>>>>>>>>>>>>>> [init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16]
>>> [init TSN:
>>>>>>>>>>>>>>>> 1877695021]
>>>>>>>>>>>>>>>> 18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>>> [COOKIE ECHO]
>>>>>>>>>>>>>>>> 18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>>> [COOKIE ACK]
>>>>>>>>>>>>>>>> 18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>>> [HB REQ]
>>>>>>>>>>>>>>>> 18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>>> [HB ACK]
>>>>>>>>>>>>>>>> 18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>>> [DATA]
>>>>>>>>>>>>>>>> (B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
>>>>>>>>>>>>>>>> 18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>>> [SACK]
>>>>>>>>>>>>>>>> [cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
>>>>>>>>>>>>>>>> 18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>>> [HB REQ]
>>>>>>>>>>>>>>>> 18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>>> [HB ACK]
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> From the observations, it seems that the LKSCTP library is
>>> not able to
>>>>>>>>>>>>>>>> use the original local address when multi-homing is being
>>> used. Is
>>>>>>>>>>>>>>>> there anyway can be resolved it?
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> Thanks
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> PS
>>>>>>>>>>>>>>>> --
>>>>>>>>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe
>>> linux-sctp" in
>>>>>>>>>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>>>>>>>>>> More majordomo info at
>>> http://vger.kernel.org/majordomo-info.html
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>> --
>>>>>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe
>>> linux-sctp" in
>>>>>>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>>>>>>> More majordomo info at
>>> http://vger.kernel.org/majordomo-info.html
>>>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> --
>>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe
>>> linux-sctp" in
>>>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>>>
>>>>>
>>>
>>>
>>
>

Re: Supporting 4 way connections in LKSCTP

[Vlad Yasevich]

On 12/03/2013 08:59 PM, Sun Paul wrote:
> This is the most puzzling area. I really not sure whether it is really
> valid or not. Is there any documented statement supporting this?
> 
> Let me summarize the behavior again.
> 
> NODE-A
> eth1: IP-A
> eth2: IP-B
> 
> NODE-B
> eth1: IP-X
> eth2: IP-Y
> 
> In normal operation, IP-A sends INIT to IP-X, IP-X returns INIT_ACK to
> IP-A. IP-A then sends HB to IP-X, IP-X then returns HB_ACK to IP-A. In
> the meantime, IP-B sends HB to IP-Y and IPY returns HB_ACK.
> 
> In case of the path between IP-A and IP-X is broken, IP-B sends INIT
> to IP-X, NODE-B uses IP-Y to return INIT_ACK to IP-B. Then IP-B sends
> HB to IP-X, and IP-Y returns HB_ACK to IP-B. In the meantime, the HB
> communication between IP-B and IP-Y follows the normal flow.
> 
> Can I confirm, is it really valid?

As long as NODE-B knows about both IP-A and IP-B, and NODE-A knows about
both IP-X and IP-Y (meaning all the addresses were exchanged inside INIT
and INIT-ACK), then this situation is perfectly valid.  In fact, this
has been tested an multiple interops.

Now, not all implementations will pick the source address you seem to
expect.  Linux, does not do source based transport selection.  It only
looks at the destination and picks the best source address based on
routing table decision.  So, in the case of Linux (nodeA), there will
only be 2 transports: one with a dest of IP-X and one with dest of IP-Y.
If it determined at start-up that IP-A is the source to set to IP-X, it
will never try to use IP-B to send to IP-X.  If it detects that
destination IP-X is unreachable, then it will keep probing, but it will
not change the source address.

Remember, HB-ACKs do not have to be returned from the same address that
HB were sent to.  This is because HB contains a nonce and that nonce
is used to locate the correct transport that this HB-ACK belongs to.

So, yes, the above communication is a valid SCTP exchange.

-vlad
> 
> On Tue, Dec 3, 2013 at 11:22 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>> On 12/03/2013 08:11 AM, Sun Paul wrote:
>>> But how about the HB and HB_ACK?  Still valid?
>>
>> As long as the source address is part of the association, then yes
>> it is perfectly valid.
>>
>> -vlad
>>
>>> On Dec 3, 2013 8:32 PM, "Vlad Yasevich" <vyasevich@gmail.com> wrote:
>>>
>>>> On 12/02/2013 09:19 PM, Sun Paul wrote:
>>>>> so in this case, says
>>>>>
>>>>> (NODE-A) IP-B send INIT to IP-X (NODE-B), and then IP-Y (NODE-B)
>>>>> returns INIT_ACK to IP-B (NODE-A)
>>>>>
>>>>> this is also treated as a valid, am I correct?
>>>>
>>>> As long as IP-X (Node-B) is present in the address list of the INIT-ACK
>>>> chunk, yes.
>>>>
>>>> There is the code in __sctp_rcv_lookup_harder() that looks for other
>>>> adddresses in the INIT and INIT-ACK chunks.
>>>>
>>>> -vlad
>>>>>
>>>>>
>>>>> On Tue, Dec 3, 2013 at 10:03 AM, Vlad Yasevich <vyasevich@gmail.com>
>>>> wrote:
>>>>>> On 12/02/2013 08:39 PM, Sun Paul wrote:
>>>>>>> Another question
>>>>>>>
>>>>>>> if a wrong source IP is used, does the association still classified as
>>>> normal?
>>>>>>
>>>>>> What do you mean my wrong source IP?  As long as the address is part of
>>>>>> the association, it can be used.
>>>>>>
>>>>>> -vlad
>>>>>>
>>>>>>>
>>>>>>> On Tue, Dec 3, 2013 at 9:31 AM, Sun Paul <paulrbk@gmail.com> wrote:
>>>>>>>> Thanks Vlad
>>>>>>>>
>>>>>>>> I checked on the route, and it looks correct.
>>>>>>>>
>>>>>>>> [root@localhost ~]# ip route get 11.1.1.1 from 110.1.1.1
>>>>>>>> 11.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
>>>>>>>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>>>>>>>
>>>>>>>> [root@localhost ~]# ip route get 11.1.1.1 from 120.1.1.1
>>>>>>>> 11.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
>>>>>>>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>>>>>>>
>>>>>>>> [root@localhost ~]# ip route get 12.1.1.1 from 120.1.1.1
>>>>>>>> 12.1.1.1 from 120.1.1.1 via 120.1.1.254 dev eth2
>>>>>>>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>>>>>>>
>>>>>>>> [root@localhost ~]# ip route get 12.1.1.1 from 110.1.1.1
>>>>>>>> 12.1.1.1 from 110.1.1.1 via 110.1.1.254 dev eth1
>>>>>>>>     cache  mtu 1500 advmss 1460 hoplimit 64
>>>>>>>>
>>>>>>>> so, if this is not being handled in LKSCTP, is it possible to suggest
>>>>>>>> a way how we can achieve it?
>>>>>>>>
>>>>>>>> On Tue, Dec 3, 2013 at 12:42 AM, Vlad Yasevich <vyasevich@gmail.com>
>>>> wrote:
>>>>>>>>> On 12/02/2013 10:45 AM, Karl Heiss wrote:
>>>>>>>>>> On Mon, Dec 2, 2013 at 9:38 AM, Vlad Yasevich <vyasevich@gmail.com>
>>>> wrote:
>>>>>>>>>>> On 11/27/2013 11:03 PM, Sun Paul wrote:
>>>>>>>>>>>> How LKSCTP select which source address to use for the INIT_ACK or
>>>>>>>>>>>> HB_ACK? below is the testing result where a router is located in
>>>> the
>>>>>>>>>>>> middle.
>>>>>>>>>>>>
>>>>>>>>>>>> Before starting the application. the packet on eth1 and eth2 are
>>>>>>>>>>>>
>>>>>>>>>>>> eth1
>>>>>>>>>>>> 0 packets dropped by kernel
>>>>>>>>>>>> [root@localhost ~]# tcpdump -i eth1 -s 0 -nn
>>>>>>>>>>>> tcpdump: verbose output suppressed, use -v or -vv for full
>>>> protocol decode
>>>>>>>>>>>> listening on eth1, link-type EN10MB (Ethernet), capture size
>>>> 65535 bytes
>>>>>>>>>>>> 11:24:14.262489 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>>>>>>>> [init tag: 28362903] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN:
>>>> 0]
>>>>>>>>>>>> 11:24:14.262522 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1)
>>>> [ABORT]
>>>>>>>>>>>> 11:24:14.539486
>>>>>>>>>>>> 11:24:16.262488 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>>>>>>>> [init tag: 29391734] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN:
>>>> 0]
>>>>>>>>>>>> 11:24:16.262520 IP 110.1.1.1.2905 > 12.1.1.1.2905: sctp (1)
>>>> [ABORT]
>>>>>>>>>>>>
>>>>>>>>>>>> eth2
>>>>>>>>>>>> [root@localhost ~]# tcpdump -i eth2 -s 0 -nn
>>>>>>>>>>>> tcpdump: verbose output suppressed, use -v or -vv for full
>>>> protocol decode
>>>>>>>>>>>> listening on eth2, link-type EN10MB (Ethernet), capture size
>>>> 65535 bytes
>>>>>>>>>>>>
>>>>>>>>>>>> When starting the application. the packet show as below.
>>>>>>>>>>>>
>>>>>>>>>>>> eth1
>>>>>>>>>>>> 11:26:02.261511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [INIT]
>>>>>>>>>>>> [init tag: 26256828] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN:
>>>> 0]
>>>>>>>>>>>> 11:26:02.263513 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1)
>>>> [COOKIE ECHO]
>>>>>>>>>>>> 11:26:02.264518 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB
>>>> REQ]
>>>>>>>>>>>> 11:26:02.563511 IP 12.1.1.1.2905 > 110.1.1.1.2905: sctp (1) [HB
>>>> REQ]
>>>>>>>>>>>>
>>>>>>>>>>>> eth2
>>>>>>>>>>>> 11:26:02.261604 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [INIT
>>>> ACK]
>>>>>>>>>>>> [init tag: 3478239387] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
>>>>>>>>>>>> 2330749678]
>>>>>>>>>>>> 11:26:02.263583 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1)
>>>> [COOKIE ACK]
>>>>>>>>>>>> 11:26:02.264548 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB
>>>> ACK]
>>>>>>>>>>>> 11:26:02.264652 IP 11.1.1.1.2905 > 120.1.1.1.2905: sctp (1) [HB
>>>> REQ]
>>>>>>>>>>>> 11:26:02.264705 IP 120.1.1.1.2905 > 11.1.1.1.2905: sctp (1) [HB
>>>> ACK]
>>>>>>>>>>>> 11:26:02.563543 IP 120.1.1.1.2905 > 12.1.1.1.2905: sctp (1) [HB
>>>> ACK]
>>>>>>>>>>>>
>>>>>>>>>>>> From the above result, you can see that the INIT, COOKIE ECHO and
>>>>>>>>>>>> HB_REQ originated from 12.1.1.1 on eth1, but the ACK (INIT_ACK,
>>>>>>>>>>>> COOKIE_ACK, HB_ACK) are returned on eth2 using source address
>>>>>>>>>>>> 120.1.1.1 instead of 110.1.1.1.
>>>>>>>>>>>>
>>>>>>>>>>>> Why LKSCTP use 120.1.1.1 as source instead of 110.1.1.1?
>>>>>>>>>>>>
>>>>>>>>>>>> For simple ICMP ping test, it is normal, but not for SCTP.
>>>>>>>>>>>>
>>>>>>>>>>>> eth1
>>>>>>>>>>>> 11:30:02.824548 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id
>>>> 37178,
>>>>>>>>>>>> seq 12, length 64
>>>>>>>>>>>> 11:30:02.824559 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id
>>>> 37178,
>>>>>>>>>>>> seq 12, length 64
>>>>>>>>>>>> 11:30:03.825551 IP 12.1.1.1 > 110.1.1.1: ICMP echo request, id
>>>> 37178,
>>>>>>>>>>>> seq 13, length 64
>>>>>>>>>>>> 11:30:03.825561 IP 110.1.1.1 > 12.1.1.1: ICMP echo reply, id
>>>> 37178,
>>>>>>>>>>>> seq 13, length 64
>>>>>>>>>>>>
>>>>>>>>>>>> eth2
>>>>>>>>>>>> 11:30:34.027687 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id
>>>> 46138,
>>>>>>>>>>>> seq 2, length 64
>>>>>>>>>>>> 11:30:34.027697 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id
>>>> 46138,
>>>>>>>>>>>> seq 2, length 64
>>>>>>>>>>>> 11:30:35.027686 IP 11.1.1.1 > 120.1.1.1: ICMP echo request, id
>>>> 46138,
>>>>>>>>>>>> seq 3, length 64
>>>>>>>>>>>> 11:30:35.027694 IP 120.1.1.1 > 11.1.1.1: ICMP echo reply, id
>>>> 46138,
>>>>>>>>>>>> seq 3, length 64
>>>>>>>>>>>>
>>>>>>>>>>>> Below is the route information
>>>>>>>>>>>> #route -n
>>>>>>>>>>>> Kernel IP routing table
>>>>>>>>>>>> Destination     Gateway         Genmask         Flags Metric Ref
>>>>    Use Iface
>>>>>>>>>>>> 110.1.1.0       0.0.0.0         255.255.255.0   U     0      0
>>>>      0 eth1
>>>>>>>>>>>> 120.1.1.0       0.0.0.0         255.255.255.0   U     0      0
>>>>      0 eth2
>>>>>>>>>>>>
>>>>>>>>>>>> # ip route show
>>>>>>>>>>>> 110.1.1.0/24 dev eth1  proto kernel  scope link  src 110.1.1.1
>>>>>>>>>>>> 120.1.1.0/24 dev eth2  proto kernel  scope link  src 120.1.1.1
>>>>>>>>>>>>
>>>>>>>>>>>> Since we are using iproute2, so we will have dedicate routing
>>>> table
>>>>>>>>>>>> per interface
>>>>>>>>>>>>
>>>>>>>>>>>> # ip route show table SCTP1
>>>>>>>>>>>> default via 110.1.1.254 dev eth1
>>>>>>>>>>>>
>>>>>>>>>>>> # ip route show table SCTP2
>>>>>>>>>>>> default via 120.1.1.254 dev eth2
>>>>>>>>>>>>
>>>>>>>>>>>> # ip rule ls
>>>>>>>>>>>> 0: from all lookup local
>>>>>>>>>>>> 101: from 110.1.1.1 lookup SCTP1
>>>>>>>>>>>> 102: from 120.1.1.1 lookup SCTP2
>>>>>>>>>>>> 32766: from all lookup main
>>>>>>>>>>>> 32767: from all lookup default
>>>>>>>>>>>>
>>>>>>>>>>>> How LKSCTP select source address to reply? If we know how it
>>>> works,
>>>>>>>>>>>> then we may know what is going wrong.
>>>>>>>>>>>
>>>>>>>>>>> LKSCTP will prefer the address returned from the routing table as
>>>> long
>>>>>>>>>>> as it is one of the addresses that is bound by the socket and are
>>>> usable
>>>>>>>>>>> by the association.
>>>>>>>>>>>
>>>>>>>>>>> If the address returned from the route lookup is not part of the
>>>>>>>>>>> association, then lksctp attempts to lookup routes using one of the
>>>>>>>>>>> source addresses it has available.  Usually the first lookup
>>>> succeeds
>>>>>>>>>>> due to the host-model implementation in linux.
>>>>>>>>>>>
>>>>>>>>>>> You may want to change your rule set to be destination based.  Then
>>>>>>>>>>> in the table associated with the rule, specify the source address
>>>>>>>>>>> you want to be used.
>>>>>>>>>>>
>>>>>>>>>>> -vlad
>>>>>>>>>>
>>>>>>>>>> I have had similar qualms myself about this behavior, and I honestly
>>>>>>>>>> don't know what the correct answer should be...
>>>>>>>>>>
>>>>>>>>>> In my opinion, shouldn't the source address "just work" for
>>>>>>>>>> acknowledgements? If the spec explicitly states that the ACK should
>>>>>>>>>> have a source address that matches the destination of the chunk
>>>> being
>>>>>>>>>> ACKed, why should someone have to configure this behavior outside of
>>>>>>>>>> the SCTP stack by default? Is it a technical limitation, or is this
>>>>>>>>>> done for a particular reason?  I can understand needing to override
>>>>>>>>>> the behavior, but why isn't the default "sane"?
>>>>>>>>>
>>>>>>>>> I think the results are sane, they simply may not match expectations.
>>>>>>>>> SCTP spec doesn't say anything about source address selection.  It
>>>>>>>>> says that a response should be send back to the source of the
>>>> request.
>>>>>>>>> This is being done in both cases, i.e. the destination address in
>>>>>>>>> INIT-ACK matches the source of the INIT.
>>>>>>>>>
>>>>>>>>> The spec does contain the MAY text that allows finer control of
>>>> source
>>>>>>>>> addresses, but lksctp doesn't seem to implement that.  Whenever we've
>>>>>>>>> tried, we couldn't get the generic mechanism working to please
>>>> everyone,
>>>>>>>>> as everyone had slightly different configurations and expectations.
>>>>  So
>>>>>>>>> we left it to the rules engine.
>>>>>>>>>
>>>>>>>>> In this setup, it just appears that the default routing is not what
>>>> you
>>>>>>>>> expect.  You can easily check this with 'ip route get' command.  If
>>>> it
>>>>>>>>> is not what you want linux allows you to change that via ip rules.
>>>>>>>>>
>>>>>>>>> -vlad
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Karl
>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> On Wed, Nov 27, 2013 at 8:45 PM, Neil Horman <
>>>> nhorman@tuxdriver.com> wrote:
>>>>>>>>>>>>> On Wed, Nov 27, 2013 at 07:10:49AM +0800, Sun Paul wrote:
>>>>>>>>>>>>>> Hi Vlad
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Thank for your reply. If it is based on the destination IP to
>>>> find the
>>>>>>>>>>>>>> best route, why the problem didn't happen on single-homing
>>>> sample?
>>>>>>>>>>>>>>
>>>>>>>>>>>>> Because You only ever use one address from NODE A (12.1.1.1)
>>>>>>>>>>>>>
>>>>>>>>>>>>>> In the single-homing sample that provided in the original
>>>> email, both
>>>>>>>>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B
>>>> during the
>>>>>>>>>>>>>> test. However, the LKSCTP library know to use the interface
>>>> eth1 to
>>>>>>>>>>>>>> respond to the SCTP request.
>>>>>>>>>>>>>>
>>>>>>>>>>>>> Yes, because it does a route lookup to each of the two ip
>>>> addresses to NODE B,
>>>>>>>>>>>>> and in both lookups, the route indicates that only one source
>>>> address should be
>>>>>>>>>>>>> used (12.1.1.1).  If you issue a ip route show command, you'll
>>>> see that routes
>>>>>>>>>>>>> to both address on NODE B match on a rule that specifies the
>>>> same src address
>>>>>>>>>>>>> and interface be used.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Neil
>>>>>>>>>>>>>
>>>>>>>>>>>>>> - PS
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> On Wed, Nov 27, 2013 at 7:09 AM, Sun Paul <paulrbk@gmail.com>
>>>> wrote:
>>>>>>>>>>>>>>> Hi Vlad
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Thank for your reply. If it is based on the destination IP to
>>>> find the
>>>>>>>>>>>>>>> best route, why the problem didn't happen on single-homing
>>>> sample?
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> In the single-homing sample that provided in the original
>>>> email, both
>>>>>>>>>>>>>>> of the interfaces (eth1 and eth2) are presented on NODE-B
>>>> during the
>>>>>>>>>>>>>>> test. However, the LKSCTP library know to use the interface
>>>> eth1 to
>>>>>>>>>>>>>>> respond to the SCTP request.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> - PS
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> On Tue, Nov 26, 2013 at 11:19 PM, Vlad Yasevich <
>>>> vyasevich@gmail.com> wrote:
>>>>>>>>>>>>>>>> On 11/25/2013 08:03 PM, Sun Paul wrote:
>>>>>>>>>>>>>>>>> Hi
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> we have a problem on using LKSCTP to form a 4 ways
>>>> multi-homing network.
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> Configuration
>>>>>>>>>>>>>>>>> - Node-A has 2 IP addresses in different subnets, known as
>>>> IP-A (eth1),
>>>>>>>>>>>>>>>>> IP-B (eth2)
>>>>>>>>>>>>>>>>> - Node-B has 2 IP addresses in different subnets, known as
>>>> IP-X (eth1),
>>>>>>>>>>>>>>>>> IP-Y (eth2)
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> First of all, this is not a 4 way multi-homed network.  As
>>>> far as each
>>>>>>>>>>>>>>>> SCTP association is concerned, it has only 2 destinations to
>>>> send to
>>>>>>>>>>>>>>>> so it has only 2 ways to get there.  The fact that you have
>>>> multiple
>>>>>>>>>>>>>>>> local addresses doesn't mean that every local address can and
>>>> should
>>>>>>>>>>>>>>>> be used to connect to the remote.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> the four way paths are shown below.
>>>>>>>>>>>>>>>>> 1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>>>>>>>>>> 2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>>>>>>>>>> 3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
>>>>>>>>>>>>>>>>> 4. IP-B (12.1.1.1) to IP-X (11.1.1.11)
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> No, actually you only have 2 paths:  one to IPX and one to
>>>> IP-Y.
>>>>>>>>>>>>>>>> Which source address you choose is based on routing policy
>>>>>>>>>>>>>>>> decisions and is outside the scope of SCTP.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> the HB/HB_ACK is normal for the paths " IP-A to IP-X" and
>>>> "IP-B to
>>>>>>>>>>>>>>>>> IP-Y", but it is not correct for the rest of two.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> Right, because linux is using a host addressing model, not an
>>>> interface
>>>>>>>>>>>>>>>> addressing model.  SCTP stack simply finds the best source
>>>> address
>>>>>>>>>>>>>>>> that can be used to reach IP-X and it happens to be IP-A.  So
>>>> that
>>>>>>>>>>>>>>>> is what it is going to use.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> The above explains why you are seeing what you describe below.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> In the end, linux SCTP implementation determines paths solely
>>>> based
>>>>>>>>>>>>>>>> on the destination address.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> -vlad
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> First of all, we are using iproute2 to form 2 table such
>>>> that when
>>>>>>>>>>>>>>>>> IP-B arrives on IP-X, it will know how to route back to IP-B
>>>> on the
>>>>>>>>>>>>>>>>> same interface, i.e (eth1). Same logic for the path "IP-A to
>>>> IP-X".
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> What we observed here is that when 12.1.1.1 sends INIT to
>>>> 11.1.1.11,
>>>>>>>>>>>>>>>>> LKSCTP will send back the INIT_ACK to 12.1.1.1 using
>>>> 12.1.1.11 but not
>>>>>>>>>>>>>>>>> using the IP 11.1.1.11.
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> The above operation makes the subsequence HB/HB_ACK in using
>>>> wrong IP address.
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> TCP trace on eth1
>>>>>>>>>>>>>>>>> 18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>>>> [INIT]
>>>>>>>>>>>>>>>>> [init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init
>>>> TSN: 0]
>>>>>>>>>>>>>>>>> 18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>>>> [COOKIE ECHO]
>>>>>>>>>>>>>>>>> 18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>>>> [HB REQ]
>>>>>>>>>>>>>>>>> 18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1)
>>>> [HB ACK]
>>>>>>>>>>>>>>>>> 18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1)
>>>> [HB ACK]
>>>>>>>>>>>>>>>>> 18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1)
>>>> [HB ACK]
>>>>>>>>>>>>>>>>> 18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1)
>>>> [HB ACK]
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> TCP trace on eth2
>>>>>>>>>>>>>>>>> 18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>>>> [INIT ACK]
>>>>>>>>>>>>>>>>> [init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init
>>>> TSN:
>>>>>>>>>>>>>>>>> 3340756356]
>>>>>>>>>>>>>>>>> 18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>>>> [COOKIE ACK]
>>>>>>>>>>>>>>>>> 18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>>>> [HB ACK]
>>>>>>>>>>>>>>>>> 18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>>>> [HB REQ]
>>>>>>>>>>>>>>>>> 18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>>>> [HB REQ]
>>>>>>>>>>>>>>>>> 18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>>>> [HB REQ]
>>>>>>>>>>>>>>>>> 18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>>>> [HB REQ]
>>>>>>>>>>>>>>>>> 18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>>>> [HB REQ]
>>>>>>>>>>>>>>>>> 18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>>>> [HB REQ]
>>>>>>>>>>>>>>>>> 18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1)
>>>> [HB REQ]
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> If we are using single homing, there is no problem on the
>>>> SCTP
>>>>>>>>>>>>>>>>> communication. Below is the TCP trace on eth1 using sctp_test
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> 18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>>>> [INIT]
>>>>>>>>>>>>>>>>> [init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init
>>>> TSN: 0]
>>>>>>>>>>>>>>>>> 18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>>>> [INIT ACK]
>>>>>>>>>>>>>>>>> [init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16]
>>>> [init TSN:
>>>>>>>>>>>>>>>>> 1877695021]
>>>>>>>>>>>>>>>>> 18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>>>> [COOKIE ECHO]
>>>>>>>>>>>>>>>>> 18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>>>> [COOKIE ACK]
>>>>>>>>>>>>>>>>> 18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>>>> [HB REQ]
>>>>>>>>>>>>>>>>> 18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>>>> [HB ACK]
>>>>>>>>>>>>>>>>> 18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>>>> [DATA]
>>>>>>>>>>>>>>>>> (B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
>>>>>>>>>>>>>>>>> 18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>>>> [SACK]
>>>>>>>>>>>>>>>>> [cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
>>>>>>>>>>>>>>>>> 18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1)
>>>> [HB REQ]
>>>>>>>>>>>>>>>>> 18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1)
>>>> [HB ACK]
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> From the observations, it seems that the LKSCTP library is
>>>> not able to
>>>>>>>>>>>>>>>>> use the original local address when multi-homing is being
>>>> used. Is
>>>>>>>>>>>>>>>>> there anyway can be resolved it?
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> Thanks
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> PS
>>>>>>>>>>>>>>>>> --
>>>>>>>>>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe
>>>> linux-sctp" in
>>>>>>>>>>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>>>>>>>>>>> More majordomo info at
>>>> http://vger.kernel.org/majordomo-info.html
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>> --
>>>>>>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe
>>>> linux-sctp" in
>>>>>>>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>>>>>>>> More majordomo info at
>>>> http://vger.kernel.org/majordomo-info.html
>>>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> --
>>>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe
>>>> linux-sctp" in
>>>>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>>>>>
>>>>>>
>>>>
>>>>
>>>
>>

RE: Supporting 4 way connections in LKSCTP

[David Laight]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="UTF-8", Size: 1935 bytes --]

> > In normal operation, IP-A sends INIT to IP-X, IP-X returns INIT_ACK to
> > IP-A. IP-A then sends HB to IP-X, IP-X then returns HB_ACK to IP-A. In
> > the meantime, IP-B sends HB to IP-Y and IPY returns HB_ACK.
> >
> > In case of the path between IP-A and IP-X is broken, IP-B sends INIT
> > to IP-X, NODE-B uses IP-Y to return INIT_ACK to IP-B. Then IP-B sends
> > HB to IP-X, and IP-Y returns HB_ACK to IP-B. In the meantime, the HB
> > communication between IP-B and IP-Y follows the normal flow.
> >
> > Can I confirm, is it really valid?
> 
> As long as NODE-B knows about both IP-A and IP-B, and NODE-A knows about
> both IP-X and IP-Y (meaning all the addresses were exchanged inside INIT
> and INIT-ACK), then this situation is perfectly valid.  In fact, this
> has been tested an multiple interops.

There are some network configurations that do cause problems.
Consider 4 systems with 3 LAN segments:
A) 10.10.10.1 on LAN X and 192.168.1.1 on LAN Y.
B) 10.10.10.2 on LAN X and 192.168.1.2 on LAN Y.
C) 10.10.10.3 on LAN X.
D) 10.10.10.4 on LAN X and 192.168.1.2 on LAN Z.
There are no routers between the networks (and none of the systems
are running IP forwarding).

If A connects to B everything is fine - traffic can use either LAN.

Connections from A to C are problematic if C tries to send anything
(except a HB) to 192.168.1.1 before receiving a HB response.
One of the SCTP stacks we've used did send messages to an
inappropriate address, but I've forgotten which one.

Connections between A and D fail unless the HB errors A receives
for 192.168.1.2 are ignored.

Of course the application could explicitly bind to only the 10.x address
but that requires the application know the exact network topology
and may be difficult for incoming calls.

	David

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Re: Supporting 4 way connections in LKSCTP

[Vlad Yasevich]

On 12/04/2013 09:50 AM, David Laight wrote:
>>> In normal operation, IP-A sends INIT to IP-X, IP-X returns INIT_ACK to
>>> IP-A. IP-A then sends HB to IP-X, IP-X then returns HB_ACK to IP-A. In
>>> the meantime, IP-B sends HB to IP-Y and IPY returns HB_ACK.
>>>
>>> In case of the path between IP-A and IP-X is broken, IP-B sends INIT
>>> to IP-X, NODE-B uses IP-Y to return INIT_ACK to IP-B. Then IP-B sends
>>> HB to IP-X, and IP-Y returns HB_ACK to IP-B. In the meantime, the HB
>>> communication between IP-B and IP-Y follows the normal flow.
>>>
>>> Can I confirm, is it really valid?
>>
>> As long as NODE-B knows about both IP-A and IP-B, and NODE-A knows about
>> both IP-X and IP-Y (meaning all the addresses were exchanged inside INIT
>> and INIT-ACK), then this situation is perfectly valid.  In fact, this
>> has been tested an multiple interops.
> 
> There are some network configurations that do cause problems.
> Consider 4 systems with 3 LAN segments:
> A) 10.10.10.1 on LAN X and 192.168.1.1 on LAN Y.
> B) 10.10.10.2 on LAN X and 192.168.1.2 on LAN Y.
> C) 10.10.10.3 on LAN X.
> D) 10.10.10.4 on LAN X and 192.168.1.2 on LAN Z.
> There are no routers between the networks (and none of the systems
> are running IP forwarding).
> 
> If A connects to B everything is fine - traffic can use either LAN.
> 
> Connections from A to C are problematic if C tries to send anything
> (except a HB) to 192.168.1.1 before receiving a HB response.
> One of the SCTP stacks we've used did send messages to an
> inappropriate address, but I've forgotten which one.

I guess that would be problematic if A can not receive traffic for
192.168.1.1 on the interface connected to LAN X.  I shouldn't
technically be a problem for C as it should mark the path to 192.168.1.1
as down.  For A, as long as it doesn't decide to ABORT the association,
it shouldn't be a problem either.  It would be interesting to know more
about what problems you've observed.

> 
> Connections between A and D fail unless the HB errors A receives
> for 192.168.1.2 are ignored.

Yes, this configuration is very error prone, especially if system B and
system D are up at the same time.  Any attempts by system A to use
LAN Y will result in an ABORT generated by system B.  I have seen
this issue well in production and we had to renumber system D to solve
it.

-vlad
> 
> Of course the application could explicitly bind to only the 10.x address
> but that requires the application know the exact network topology
> and may be difficult for incoming calls.
> 
> 	David
> 

Re: Supporting 4 way connections in LKSCTP

[Michael Tuexen]

On Dec 4, 2013, at 4:41 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:

> On 12/04/2013 09:50 AM, David Laight wrote:
>>>> In normal operation, IP-A sends INIT to IP-X, IP-X returns INIT_ACK to
>>>> IP-A. IP-A then sends HB to IP-X, IP-X then returns HB_ACK to IP-A. In
>>>> the meantime, IP-B sends HB to IP-Y and IPY returns HB_ACK.
>>>> 
>>>> In case of the path between IP-A and IP-X is broken, IP-B sends INIT
>>>> to IP-X, NODE-B uses IP-Y to return INIT_ACK to IP-B. Then IP-B sends
>>>> HB to IP-X, and IP-Y returns HB_ACK to IP-B. In the meantime, the HB
>>>> communication between IP-B and IP-Y follows the normal flow.
>>>> 
>>>> Can I confirm, is it really valid?
>>> 
>>> As long as NODE-B knows about both IP-A and IP-B, and NODE-A knows about
>>> both IP-X and IP-Y (meaning all the addresses were exchanged inside INIT
>>> and INIT-ACK), then this situation is perfectly valid.  In fact, this
>>> has been tested an multiple interops.
>> 
>> There are some network configurations that do cause problems.
>> Consider 4 systems with 3 LAN segments:
>> A) 10.10.10.1 on LAN X and 192.168.1.1 on LAN Y.
>> B) 10.10.10.2 on LAN X and 192.168.1.2 on LAN Y.
>> C) 10.10.10.3 on LAN X.
>> D) 10.10.10.4 on LAN X and 192.168.1.2 on LAN Z.
>> There are no routers between the networks (and none of the systems
>> are running IP forwarding).
>> 
>> If A connects to B everything is fine - traffic can use either LAN.
>> 
>> Connections from A to C are problematic if C tries to send anything
>> (except a HB) to 192.168.1.1 before receiving a HB response.
>> One of the SCTP stacks we've used did send messages to an
>> inappropriate address, but I've forgotten which one.
> 
> I guess that would be problematic if A can not receive traffic for
> 192.168.1.1 on the interface connected to LAN X.  I shouldn't
> technically be a problem for C as it should mark the path to 192.168.1.1
> as down.  For A, as long as it doesn't decide to ABORT the association,
> it shouldn't be a problem either.  It would be interesting to know more
> about what problems you've observed.
> 
>> 
>> Connections between A and D fail unless the HB errors A receives
>> for 192.168.1.2 are ignored.
> 
> Yes, this configuration is very error prone, especially if system B and
> system D are up at the same time.  Any attempts by system A to use
> LAN Y will result in an ABORT generated by system B.  I have seen
> this issue well in production and we had to renumber system D to solve
> it.
The point is that address scoping should be used. When sending an
INIT from 10.10.10.1 to 10.10.10.4 you should not list 192.168.1.1,
since you are transmitting an address to a node which might or might
not "be in the same scope". We had IDs for that in the past, but
they never made it to RFC state, because they were not progressed enough
by the authors. Maybe we should push them again...

Best regards
Michael
> 
> -vlad
>> 
>> Of course the application could explicitly bind to only the 10.x address
>> but that requires the application know the exact network topology
>> and may be difficult for incoming calls.
>> 
>> 	David
>> 
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

Re: Supporting 4 way connections in LKSCTP

[Vlad Yasevich]

On 12/04/2013 11:01 AM, Michael Tuexen wrote:
> On Dec 4, 2013, at 4:41 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
> 
>> On 12/04/2013 09:50 AM, David Laight wrote:
>>>>> In normal operation, IP-A sends INIT to IP-X, IP-X returns INIT_ACK to
>>>>> IP-A. IP-A then sends HB to IP-X, IP-X then returns HB_ACK to IP-A. In
>>>>> the meantime, IP-B sends HB to IP-Y and IPY returns HB_ACK.
>>>>>
>>>>> In case of the path between IP-A and IP-X is broken, IP-B sends INIT
>>>>> to IP-X, NODE-B uses IP-Y to return INIT_ACK to IP-B. Then IP-B sends
>>>>> HB to IP-X, and IP-Y returns HB_ACK to IP-B. In the meantime, the HB
>>>>> communication between IP-B and IP-Y follows the normal flow.
>>>>>
>>>>> Can I confirm, is it really valid?
>>>>
>>>> As long as NODE-B knows about both IP-A and IP-B, and NODE-A knows about
>>>> both IP-X and IP-Y (meaning all the addresses were exchanged inside INIT
>>>> and INIT-ACK), then this situation is perfectly valid.  In fact, this
>>>> has been tested an multiple interops.
>>>
>>> There are some network configurations that do cause problems.
>>> Consider 4 systems with 3 LAN segments:
>>> A) 10.10.10.1 on LAN X and 192.168.1.1 on LAN Y.
>>> B) 10.10.10.2 on LAN X and 192.168.1.2 on LAN Y.
>>> C) 10.10.10.3 on LAN X.
>>> D) 10.10.10.4 on LAN X and 192.168.1.2 on LAN Z.
>>> There are no routers between the networks (and none of the systems
>>> are running IP forwarding).
>>>
>>> If A connects to B everything is fine - traffic can use either LAN.
>>>
>>> Connections from A to C are problematic if C tries to send anything
>>> (except a HB) to 192.168.1.1 before receiving a HB response.
>>> One of the SCTP stacks we've used did send messages to an
>>> inappropriate address, but I've forgotten which one.
>>
>> I guess that would be problematic if A can not receive traffic for
>> 192.168.1.1 on the interface connected to LAN X.  I shouldn't
>> technically be a problem for C as it should mark the path to 192.168.1.1
>> as down.  For A, as long as it doesn't decide to ABORT the association,
>> it shouldn't be a problem either.  It would be interesting to know more
>> about what problems you've observed.
>>
>>>
>>> Connections between A and D fail unless the HB errors A receives
>>> for 192.168.1.2 are ignored.
>>
>> Yes, this configuration is very error prone, especially if system B and
>> system D are up at the same time.  Any attempts by system A to use
>> LAN Y will result in an ABORT generated by system B.  I have seen
>> this issue well in production and we had to renumber system D to solve
>> it.
> The point is that address scoping should be used. When sending an
> INIT from 10.10.10.1 to 10.10.10.4 you should not list 192.168.1.1,
> since you are transmitting an address to a node which might or might
> not "be in the same scope". We had IDs for that in the past, but
> they never made it to RFC state, because they were not progressed enough
> by the authors. Maybe we should push them again...

But these 2 are technically in the same scope.  They are both private
address types.  Also, this will not solve the problem either since
the configured addresses could be:
System A) 10.0.0.1 on Lan X, 10.10.0.1 on Lan Y
System B) 10.0.0.2 on Lan X, 10.10.0.2 on Lan Y
System C) 10.0.0.3 on Lan X, 10.10.0.2 on Lan Z

Same problem will occur.

Btw, were there any IDs other then draft-stewart-tsvwg-sctp-ipv4?

Thanks
-vlad

> 
> Best regards
> Michael
>>
>> -vlad
>>>
>>> Of course the application could explicitly bind to only the 10.x address
>>> but that requires the application know the exact network topology
>>> and may be difficult for incoming calls.
>>>
>>> 	David
>>>
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
> 

RE: Supporting 4 way connections in LKSCTP

[David Laight]

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> > There are some network configurations that do cause problems.
> > Consider 4 systems with 3 LAN segments:
> > A) 10.10.10.1 on LAN X and 192.168.1.1 on LAN Y.
> > B) 10.10.10.2 on LAN X and 192.168.1.2 on LAN Y.
> > C) 10.10.10.3 on LAN X.
> > D) 10.10.10.4 on LAN X and 192.168.1.2 on LAN Z.
> > There are no routers between the networks (and none of the systems
> > are running IP forwarding).
> >
> > If A connects to B everything is fine - traffic can use either LAN.
> >
> > Connections from A to C are problematic if C tries to send anything
> > (except a HB) to 192.168.1.1 before receiving a HB response.
> > One of the SCTP stacks we've used did send messages to an
> > inappropriate address, but I've forgotten which one.
> 
> I guess that would be problematic if A can not receive traffic for
> 192.168.1.1 on the interface connected to LAN X.  I shouldn't
> technically be a problem for C as it should mark the path to 192.168.1.1
> as down.  For A, as long as it doesn't decide to ABORT the association,
> it shouldn't be a problem either.  It would be interesting to know more
> about what problems you've observed.

It was a long time ago, we don't actually do much SCTP testing even though
our product (SS7 M3UA) uses it. Mostly because we don't want to find
bugs that are hard to fix!

What we saw was C using the 192.x address (as supplied in the INIT) and
these not being routable to A (and not getting a response from a 3rd system).
So the application layer immediately timed everything out.

What I can't remember is whether this was Linux, Solaris or the SCTP stack
we took from freebsd and rammed into the windows kernel.

	David

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Re: Supporting 4 way connections in LKSCTP

[Michael Tuexen]

On Dec 4, 2013, at 5:12 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:

> On 12/04/2013 11:01 AM, Michael Tuexen wrote:
>> On Dec 4, 2013, at 4:41 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>> 
>>> On 12/04/2013 09:50 AM, David Laight wrote:
>>>>>> In normal operation, IP-A sends INIT to IP-X, IP-X returns INIT_ACK to
>>>>>> IP-A. IP-A then sends HB to IP-X, IP-X then returns HB_ACK to IP-A. In
>>>>>> the meantime, IP-B sends HB to IP-Y and IPY returns HB_ACK.
>>>>>> 
>>>>>> In case of the path between IP-A and IP-X is broken, IP-B sends INIT
>>>>>> to IP-X, NODE-B uses IP-Y to return INIT_ACK to IP-B. Then IP-B sends
>>>>>> HB to IP-X, and IP-Y returns HB_ACK to IP-B. In the meantime, the HB
>>>>>> communication between IP-B and IP-Y follows the normal flow.
>>>>>> 
>>>>>> Can I confirm, is it really valid?
>>>>> 
>>>>> As long as NODE-B knows about both IP-A and IP-B, and NODE-A knows about
>>>>> both IP-X and IP-Y (meaning all the addresses were exchanged inside INIT
>>>>> and INIT-ACK), then this situation is perfectly valid.  In fact, this
>>>>> has been tested an multiple interops.
>>>> 
>>>> There are some network configurations that do cause problems.
>>>> Consider 4 systems with 3 LAN segments:
>>>> A) 10.10.10.1 on LAN X and 192.168.1.1 on LAN Y.
>>>> B) 10.10.10.2 on LAN X and 192.168.1.2 on LAN Y.
>>>> C) 10.10.10.3 on LAN X.
>>>> D) 10.10.10.4 on LAN X and 192.168.1.2 on LAN Z.
>>>> There are no routers between the networks (and none of the systems
>>>> are running IP forwarding).
>>>> 
>>>> If A connects to B everything is fine - traffic can use either LAN.
>>>> 
>>>> Connections from A to C are problematic if C tries to send anything
>>>> (except a HB) to 192.168.1.1 before receiving a HB response.
>>>> One of the SCTP stacks we've used did send messages to an
>>>> inappropriate address, but I've forgotten which one.
>>> 
>>> I guess that would be problematic if A can not receive traffic for
>>> 192.168.1.1 on the interface connected to LAN X.  I shouldn't
>>> technically be a problem for C as it should mark the path to 192.168.1.1
>>> as down.  For A, as long as it doesn't decide to ABORT the association,
>>> it shouldn't be a problem either.  It would be interesting to know more
>>> about what problems you've observed.
>>> 
>>>> 
>>>> Connections between A and D fail unless the HB errors A receives
>>>> for 192.168.1.2 are ignored.
>>> 
>>> Yes, this configuration is very error prone, especially if system B and
>>> system D are up at the same time.  Any attempts by system A to use
>>> LAN Y will result in an ABORT generated by system B.  I have seen
>>> this issue well in production and we had to renumber system D to solve
>>> it.
>> The point is that address scoping should be used. When sending an
>> INIT from 10.10.10.1 to 10.10.10.4 you should not list 192.168.1.1,
>> since you are transmitting an address to a node which might or might
>> not "be in the same scope". We had IDs for that in the past, but
>> they never made it to RFC state, because they were not progressed enough
>> by the authors. Maybe we should push them again...
> 
> But these 2 are technically in the same scope.  They are both private
> address types.  Also, this will not solve the problem either since
That is correct. But I think you should not transfer a private address
to another private address belonging to a different network.
I don't think this was specified in the older IDs...
> the configured addresses could be:
> System A) 10.0.0.1 on Lan X, 10.10.0.1 on Lan Y
> System B) 10.0.0.2 on Lan X, 10.10.0.2 on Lan Y
> System C) 10.0.0.3 on Lan X, 10.10.0.2 on Lan Z
> 
> Same problem will occur.
Depending on the subnet masks, it might work not not. Are you
configuring them with /8? 
> 
> Btw, were there any IDs other then draft-stewart-tsvwg-sctp-ipv4?
Yes, one for IPv6.
http://tools.ietf.org/html/draft-stewart-tsvwg-sctpipv6-01
They need to be integrated and improved...

Best regards
Michael
> 
> Thanks
> -vlad
> 
>> 
>> Best regards
>> Michael
>>> 
>>> -vlad
>>>> 
>>>> Of course the application could explicitly bind to only the 10.x address
>>>> but that requires the application know the exact network topology
>>>> and may be difficult for incoming calls.
>>>> 
>>>> 	David
>>>> 
>>> 
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>> 
>> 
> 
> 

RE: Supporting 4 way connections in LKSCTP

[David Laight]

> The point is that address scoping should be used. When sending an
> INIT from 10.10.10.1 to 10.10.10.4 you should not list 192.168.1.1,
> since you are transmitting an address to a node which might or might
> not "be in the same scope".

You might have two machines that are connected via the public
internet and also via a private network.
The two sets of cabling being completely separate giving you
resilience to network failure.
In which case you definitely don't want address scoping.

While you may not want the SCTP traffic on the public network
itself, it could easily be routed separately.

We have systems that 'sort of' designate one interface for SIP/RTP
and the other for 'management'. They might run M3UA/SCTP but no one
has really thought enough about which interface(s) the M3UA traffic
should use.
(Think of an ISUP/SIP gateway using M3UA for ISUP signalling.)

	David

Re: Supporting 4 way connections in LKSCTP

[Michael Tuexen]

On Dec 4, 2013, at 5:48 PM, David Laight <David.Laight@ACULAB.COM> wrote:

>> The point is that address scoping should be used. When sending an
>> INIT from 10.10.10.1 to 10.10.10.4 you should not list 192.168.1.1,
>> since you are transmitting an address to a node which might or might
>> not "be in the same scope".
> 
> You might have two machines that are connected via the public
> internet and also via a private network.
> The two sets of cabling being completely separate giving you
> resilience to network failure.
> In which case you definitely don't want address scoping.
Well, if you give the SCTP stack a hint when initiating
the association, it can do the right thing.
Calling sctp_connect(private_address) should work. It will list
the public address without any problems.
One can debate that sctp_connectx(private_address, public_address)
will result in sending an INIT to the public_address listing the
private one. However, calling sctp_connect(public_address) should
not list the private_address.

Best regards
Michael
> 
> While you may not want the SCTP traffic on the public network
> itself, it could easily be routed separately.
> 
> We have systems that 'sort of' designate one interface for SIP/RTP
> and the other for 'management'. They might run M3UA/SCTP but no one
> has really thought enough about which interface(s) the M3UA traffic
> should use.
> (Think of an ISUP/SIP gateway using M3UA for ISUP signalling.)
> 
> 	David
> 
> 
> 
> 

Re: Supporting 4 way connections in LKSCTP

[Vlad Yasevich]

On 12/04/2013 12:57 PM, Sun Paul wrote:
> As I know, the A to C and A to D case must have a router in between to form
> SCTP multihome topology.

Not necessary.  I've produced proper multihoming topologies with just
VLANs and different subnet assignment.  You can even remove VLANs
if you correctly set your arp_ignore and arp_announce values.

-vlad

> On Dec 4, 2013 10:51 PM, "David Laight" <David.Laight@aculab.com> wrote:
> 
>>>> In normal operation, IP-A sends INIT to IP-X, IP-X returns INIT_ACK to
>>>> IP-A. IP-A then sends HB to IP-X, IP-X then returns HB_ACK to IP-A. In
>>>> the meantime, IP-B sends HB to IP-Y and IPY returns HB_ACK.
>>>>
>>>> In case of the path between IP-A and IP-X is broken, IP-B sends INIT
>>>> to IP-X, NODE-B uses IP-Y to return INIT_ACK to IP-B. Then IP-B sends
>>>> HB to IP-X, and IP-Y returns HB_ACK to IP-B. In the meantime, the HB
>>>> communication between IP-B and IP-Y follows the normal flow.
>>>>
>>>> Can I confirm, is it really valid?
>>>
>>> As long as NODE-B knows about both IP-A and IP-B, and NODE-A knows about
>>> both IP-X and IP-Y (meaning all the addresses were exchanged inside INIT
>>> and INIT-ACK), then this situation is perfectly valid.  In fact, this
>>> has been tested an multiple interops.
>>
>> There are some network configurations that do cause problems.
>> Consider 4 systems with 3 LAN segments:
>> A) 10.10.10.1 on LAN X and 192.168.1.1 on LAN Y.
>> B) 10.10.10.2 on LAN X and 192.168.1.2 on LAN Y.
>> C) 10.10.10.3 on LAN X.
>> D) 10.10.10.4 on LAN X and 192.168.1.2 on LAN Z.
>> There are no routers between the networks (and none of the systems
>> are running IP forwarding).
>>
>> If A connects to B everything is fine - traffic can use either LAN.
>>
>> Connections from A to C are problematic if C tries to send anything
>> (except a HB) to 192.168.1.1 before receiving a HB response.
>> One of the SCTP stacks we've used did send messages to an
>> inappropriate address, but I've forgotten which one.
>>
>> Connections between A and D fail unless the HB errors A receives
>> for 192.168.1.2 are ignored.
>>
>> Of course the application could explicitly bind to only the 10.x address
>> but that requires the application know the exact network topology
>> and may be difficult for incoming calls.
>>
>>         David
>>
>>
> 

Re: Supporting 4 way connections in LKSCTP

[Vlad Yasevich]

On 12/04/2013 11:25 AM, Michael Tuexen wrote:
> On Dec 4, 2013, at 5:12 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
> 
>> On 12/04/2013 11:01 AM, Michael Tuexen wrote:
>>> On Dec 4, 2013, at 4:41 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>
>>>> On 12/04/2013 09:50 AM, David Laight wrote:
>>>>>>> In normal operation, IP-A sends INIT to IP-X, IP-X returns INIT_ACK to
>>>>>>> IP-A. IP-A then sends HB to IP-X, IP-X then returns HB_ACK to IP-A. In
>>>>>>> the meantime, IP-B sends HB to IP-Y and IPY returns HB_ACK.
>>>>>>>
>>>>>>> In case of the path between IP-A and IP-X is broken, IP-B sends INIT
>>>>>>> to IP-X, NODE-B uses IP-Y to return INIT_ACK to IP-B. Then IP-B sends
>>>>>>> HB to IP-X, and IP-Y returns HB_ACK to IP-B. In the meantime, the HB
>>>>>>> communication between IP-B and IP-Y follows the normal flow.
>>>>>>>
>>>>>>> Can I confirm, is it really valid?
>>>>>>
>>>>>> As long as NODE-B knows about both IP-A and IP-B, and NODE-A knows about
>>>>>> both IP-X and IP-Y (meaning all the addresses were exchanged inside INIT
>>>>>> and INIT-ACK), then this situation is perfectly valid.  In fact, this
>>>>>> has been tested an multiple interops.
>>>>>
>>>>> There are some network configurations that do cause problems.
>>>>> Consider 4 systems with 3 LAN segments:
>>>>> A) 10.10.10.1 on LAN X and 192.168.1.1 on LAN Y.
>>>>> B) 10.10.10.2 on LAN X and 192.168.1.2 on LAN Y.
>>>>> C) 10.10.10.3 on LAN X.
>>>>> D) 10.10.10.4 on LAN X and 192.168.1.2 on LAN Z.
>>>>> There are no routers between the networks (and none of the systems
>>>>> are running IP forwarding).
>>>>>
>>>>> If A connects to B everything is fine - traffic can use either LAN.
>>>>>
>>>>> Connections from A to C are problematic if C tries to send anything
>>>>> (except a HB) to 192.168.1.1 before receiving a HB response.
>>>>> One of the SCTP stacks we've used did send messages to an
>>>>> inappropriate address, but I've forgotten which one.
>>>>
>>>> I guess that would be problematic if A can not receive traffic for
>>>> 192.168.1.1 on the interface connected to LAN X.  I shouldn't
>>>> technically be a problem for C as it should mark the path to 192.168.1.1
>>>> as down.  For A, as long as it doesn't decide to ABORT the association,
>>>> it shouldn't be a problem either.  It would be interesting to know more
>>>> about what problems you've observed.
>>>>
>>>>>
>>>>> Connections between A and D fail unless the HB errors A receives
>>>>> for 192.168.1.2 are ignored.
>>>>
>>>> Yes, this configuration is very error prone, especially if system B and
>>>> system D are up at the same time.  Any attempts by system A to use
>>>> LAN Y will result in an ABORT generated by system B.  I have seen
>>>> this issue well in production and we had to renumber system D to solve
>>>> it.
>>> The point is that address scoping should be used. When sending an
>>> INIT from 10.10.10.1 to 10.10.10.4 you should not list 192.168.1.1,
>>> since you are transmitting an address to a node which might or might
>>> not "be in the same scope". We had IDs for that in the past, but
>>> they never made it to RFC state, because they were not progressed enough
>>> by the authors. Maybe we should push them again...
>>
>> But these 2 are technically in the same scope.  They are both private
>> address types.  Also, this will not solve the problem either since
> That is correct. But I think you should not transfer a private address
> to another private address belonging to a different network.
> I don't think this was specified in the older IDs...
>> the configured addresses could be:
>> System A) 10.0.0.1 on Lan X, 10.10.0.1 on Lan Y
>> System B) 10.0.0.2 on Lan X, 10.10.0.2 on Lan Y
>> System C) 10.0.0.3 on Lan X, 10.10.0.2 on Lan Z
>>
>> Same problem will occur.
> Depending on the subnet masks, it might work not not. Are you
> configuring them with /8? 

No, /16 :).  With that, Sys A talking to Sys C will get an abort
from Sys B when trying to talk to 10.10.0.2.  With /8, it'll be
even worse since SysB and SysC will have duplicate addresses
within the subnet. :)

The point is that you don't always know that the same private subnet
is in reality 2 different subnets with duplicate addresses.

I've had to debug an actual production issue similar to this where
customer had a very similar configuration to above, and their
associations kept getting aborted.  When I tried accessing the
system that kept sending aborts, I found it was some windows
server and not a Diameter station they were expecting.

>>
>> Btw, were there any IDs other then draft-stewart-tsvwg-sctp-ipv4?
> Yes, one for IPv6.
> http://tools.ietf.org/html/draft-stewart-tsvwg-sctpipv6-01
> They need to be integrated and improved...
> 

Ok.  I'll take a look.

Thanks
-vlad

> Best regards
> Michael
>>
>> Thanks
>> -vlad
>>
>>>
>>> Best regards
>>> Michael
>>>>
>>>> -vlad
>>>>>
>>>>> Of course the application could explicitly bind to only the 10.x address
>>>>> but that requires the application know the exact network topology
>>>>> and may be difficult for incoming calls.
>>>>>
>>>>> 	David
>>>>>
>>>>
>>>> --
>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>> the body of a message to majordomo@vger.kernel.org
>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>
>>>
>>
>>
> 

Re: Supporting 4 way connections in LKSCTP

[Michael Tuexen]

On Dec 4, 2013, at 7:23 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:

> On 12/04/2013 11:25 AM, Michael Tuexen wrote:
>> On Dec 4, 2013, at 5:12 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>> 
>>> On 12/04/2013 11:01 AM, Michael Tuexen wrote:
>>>> On Dec 4, 2013, at 4:41 PM, Vlad Yasevich <vyasevich@gmail.com> wrote:
>>>> 
>>>>> On 12/04/2013 09:50 AM, David Laight wrote:
>>>>>>>> In normal operation, IP-A sends INIT to IP-X, IP-X returns INIT_ACK to
>>>>>>>> IP-A. IP-A then sends HB to IP-X, IP-X then returns HB_ACK to IP-A. In
>>>>>>>> the meantime, IP-B sends HB to IP-Y and IPY returns HB_ACK.
>>>>>>>> 
>>>>>>>> In case of the path between IP-A and IP-X is broken, IP-B sends INIT
>>>>>>>> to IP-X, NODE-B uses IP-Y to return INIT_ACK to IP-B. Then IP-B sends
>>>>>>>> HB to IP-X, and IP-Y returns HB_ACK to IP-B. In the meantime, the HB
>>>>>>>> communication between IP-B and IP-Y follows the normal flow.
>>>>>>>> 
>>>>>>>> Can I confirm, is it really valid?
>>>>>>> 
>>>>>>> As long as NODE-B knows about both IP-A and IP-B, and NODE-A knows about
>>>>>>> both IP-X and IP-Y (meaning all the addresses were exchanged inside INIT
>>>>>>> and INIT-ACK), then this situation is perfectly valid.  In fact, this
>>>>>>> has been tested an multiple interops.
>>>>>> 
>>>>>> There are some network configurations that do cause problems.
>>>>>> Consider 4 systems with 3 LAN segments:
>>>>>> A) 10.10.10.1 on LAN X and 192.168.1.1 on LAN Y.
>>>>>> B) 10.10.10.2 on LAN X and 192.168.1.2 on LAN Y.
>>>>>> C) 10.10.10.3 on LAN X.
>>>>>> D) 10.10.10.4 on LAN X and 192.168.1.2 on LAN Z.
>>>>>> There are no routers between the networks (and none of the systems
>>>>>> are running IP forwarding).
>>>>>> 
>>>>>> If A connects to B everything is fine - traffic can use either LAN.
>>>>>> 
>>>>>> Connections from A to C are problematic if C tries to send anything
>>>>>> (except a HB) to 192.168.1.1 before receiving a HB response.
>>>>>> One of the SCTP stacks we've used did send messages to an
>>>>>> inappropriate address, but I've forgotten which one.
>>>>> 
>>>>> I guess that would be problematic if A can not receive traffic for
>>>>> 192.168.1.1 on the interface connected to LAN X.  I shouldn't
>>>>> technically be a problem for C as it should mark the path to 192.168.1.1
>>>>> as down.  For A, as long as it doesn't decide to ABORT the association,
>>>>> it shouldn't be a problem either.  It would be interesting to know more
>>>>> about what problems you've observed.
>>>>> 
>>>>>> 
>>>>>> Connections between A and D fail unless the HB errors A receives
>>>>>> for 192.168.1.2 are ignored.
>>>>> 
>>>>> Yes, this configuration is very error prone, especially if system B and
>>>>> system D are up at the same time.  Any attempts by system A to use
>>>>> LAN Y will result in an ABORT generated by system B.  I have seen
>>>>> this issue well in production and we had to renumber system D to solve
>>>>> it.
>>>> The point is that address scoping should be used. When sending an
>>>> INIT from 10.10.10.1 to 10.10.10.4 you should not list 192.168.1.1,
>>>> since you are transmitting an address to a node which might or might
>>>> not "be in the same scope". We had IDs for that in the past, but
>>>> they never made it to RFC state, because they were not progressed enough
>>>> by the authors. Maybe we should push them again...
>>> 
>>> But these 2 are technically in the same scope.  They are both private
>>> address types.  Also, this will not solve the problem either since
>> That is correct. But I think you should not transfer a private address
>> to another private address belonging to a different network.
>> I don't think this was specified in the older IDs...
>>> the configured addresses could be:
>>> System A) 10.0.0.1 on Lan X, 10.10.0.1 on Lan Y
>>> System B) 10.0.0.2 on Lan X, 10.10.0.2 on Lan Y
>>> System C) 10.0.0.3 on Lan X, 10.10.0.2 on Lan Z
>>> 
>>> Same problem will occur.
>> Depending on the subnet masks, it might work not not. Are you
>> configuring them with /8? 
> 
> No, /16 :).  With that, Sys A talking to Sys C will get an abort
> from Sys B when trying to talk to 10.10.0.2.  With /8, it'll be
> even worse since SysB and SysC will have duplicate addresses
> within the subnet. :)
> 
> The point is that you don't always know that the same private subnet
> is in reality 2 different subnets with duplicate addresses.
I agree, you can't do it perfectly right. But you can provide some
protection.
> 
> I've had to debug an actual production issue similar to this where
> customer had a very similar configuration to above, and their
> associations kept getting aborted.  When I tried accessing the
> system that kept sending aborts, I found it was some windows
> server and not a Diameter station they were expecting.
Interesting... Availability of SCTP on Windows is quite limited...
But people seem to use SCTP on Windows.

Best regards
Michael
> 
>>> 
>>> Btw, were there any IDs other then draft-stewart-tsvwg-sctp-ipv4?
>> Yes, one for IPv6.
>> http://tools.ietf.org/html/draft-stewart-tsvwg-sctpipv6-01
>> They need to be integrated and improved...
>> 
> 
> Ok.  I'll take a look.
> 
> Thanks
> -vlad
> 
>> Best regards
>> Michael
>>> 
>>> Thanks
>>> -vlad
>>> 
>>>> 
>>>> Best regards
>>>> Michael
>>>>> 
>>>>> -vlad
>>>>>> 
>>>>>> Of course the application could explicitly bind to only the 10.x address
>>>>>> but that requires the application know the exact network topology
>>>>>> and may be difficult for incoming calls.
>>>>>> 
>>>>>> 	David
>>>>>> 
>>>>> 
>>>>> --
>>>>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>>>>> the body of a message to majordomo@vger.kernel.org
>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>> 
>>>> 
>>> 
>>> 
>> 
> 
> 

RE: Supporting 4 way connections in LKSCTP

[David Laight]

> >> the configured addresses could be:
> >> System A) 10.0.0.1 on Lan X, 10.10.0.1 on Lan Y
> >> System B) 10.0.0.2 on Lan X, 10.10.0.2 on Lan Y
> >> System C) 10.0.0.3 on Lan X, 10.10.0.2 on Lan Z
> >>
> >> Same problem will occur.
...
> With that, Sys A talking to Sys C will get an abort
> from Sys B when trying to talk to 10.10.0.2.  With /8, it'll be
> even worse since SysB and SysC will have duplicate addresses
> within the subnet. :)
> 
> The point is that you don't always know that the same private subnet
> is in reality 2 different subnets with duplicate addresses.
> 
> I've had to debug an actual production issue similar to this where
> customer had a very similar configuration to above, and their
> associations kept getting aborted.  When I tried accessing the
> system that kept sending aborts, I found it was some windows
> server and not a Diameter station they were expecting.

Does seem that the addresses listed in INIT and INIT_ACK chunks
should be ignored until a valid HB response has been received.
If an abort is received before a valid HB response then the
address should be ignored rather than the connection aborted.
Then it wouldn't matter anywhere near as much if addresses are
advertised that are not reachable from the remote system.

All this should have been thought about when the original RFC
was written.

	David

Re: Supporting 4 way connections in LKSCTP

[Michael Tuexen]

On Dec 5, 2013, at 10:35 AM, David Laight <David.Laight@ACULAB.COM> wrote:

>>>> the configured addresses could be:
>>>> System A) 10.0.0.1 on Lan X, 10.10.0.1 on Lan Y
>>>> System B) 10.0.0.2 on Lan X, 10.10.0.2 on Lan Y
>>>> System C) 10.0.0.3 on Lan X, 10.10.0.2 on Lan Z
>>>> 
>>>> Same problem will occur.
> ...
>> With that, Sys A talking to Sys C will get an abort
>> from Sys B when trying to talk to 10.10.0.2.  With /8, it'll be
>> even worse since SysB and SysC will have duplicate addresses
>> within the subnet. :)
>> 
>> The point is that you don't always know that the same private subnet
>> is in reality 2 different subnets with duplicate addresses.
>> 
>> I've had to debug an actual production issue similar to this where
>> customer had a very similar configuration to above, and their
>> associations kept getting aborted.  When I tried accessing the
>> system that kept sending aborts, I found it was some windows
>> server and not a Diameter station they were expecting.
> 
> Does seem that the addresses listed in INIT and INIT_ACK chunks
> should be ignored until a valid HB response has been received.
You are not allowed to send DATA to them until they are confirmed.
> If an abort is received before a valid HB response then the
> address should be ignored rather than the connection aborted.
No.
> Then it wouldn't matter anywhere near as much if addresses are
> advertised that are not reachable from the remote system.
> 
> All this should have been thought about when the original RFC
> was written.
Scoping wasn't considered that much, same as NAT traversal.
The assumption was that in SIGTRAN networks no NAT boxes are
deployed and you use appropriate addressing (for redundancy).

Best regards
Michael
> 
> 	David
> 
> 
> 
> 

Re: Supporting 4 way connections in LKSCTP

[Sun Paul]

So, can I get confirmation that whether we can enhance to support the
scenarios or any resolution on providing the correct routing?

On Tue, Nov 26, 2013 at 9:03 AM, Sun Paul <paulrbk@gmail.com> wrote:
> Hi
>
> we have a problem on using LKSCTP to form a 4 ways multi-homing network.
>
> Configuration
> - Node-A has 2 IP addresses in different subnets, known as IP-A (eth1),
> IP-B (eth2)
> - Node-B has 2 IP addresses in different subnets, known as IP-X (eth1),
> IP-Y (eth2)
>
> the four way paths are shown below.
> 1. IP-A (11.1.1.1) to IP-X (11.1.1.11)
> 2. IP-B (12.1.1.1) to IP-Y (12.1.1.11)
> 3. IP-A (11.1.1.1) to IP-Y (12.1.1.11)
> 4. IP-B (12.1.1.1) to IP-X (11.1.1.11)
>
> the HB/HB_ACK is normal for the paths " IP-A to IP-X" and "IP-B to
> IP-Y", but it is not correct for the rest of two.
>
> First of all, we are using iproute2 to form 2 table such that when
> IP-B arrives on IP-X, it will know how to route back to IP-B on the
> same interface, i.e (eth1). Same logic for the path "IP-A to IP-X".
>
> What we observed here is that when 12.1.1.1 sends INIT to 11.1.1.11,
> LKSCTP will send back the INIT_ACK to 12.1.1.1 using 12.1.1.11 but not
> using the IP 11.1.1.11.
>
> The above operation makes the subsequence HB/HB_ACK in using wrong IP address.
>
> TCP trace on eth1
> 18:02:41.058640 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
> [init tag: 19933036] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
> 18:02:41.061634 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
> 18:02:41.062642 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
> 18:02:41.062846 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
> 18:02:41.361811 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
> 18:02:41.661791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
> 18:02:41.961791 IP 11.1.1.11.2905 > 11.1.1.1.2905: sctp (1) [HB ACK]
>
> TCP trace on eth2
> 18:02:41.058755 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
> [init tag: 424726157] [rwnd: 131072] [OS: 5] [MIS: 5] [init TSN:
> 3340756356]
> 18:02:41.061696 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
> 18:02:41.062663 IP 12.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
> 18:02:41.062791 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
> 18:02:41.361777 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
> 18:02:41.661772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
> 18:02:41.961772 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
> 18:02:42.161771 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
> 18:02:42.461770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
> 18:02:42.675770 IP 11.1.1.1.2905 > 12.1.1.11.2905: sctp (1) [HB REQ]
>
>
> If we are using single homing, there is no problem on the SCTP
> communication. Below is the TCP trace on eth1 using sctp_test
>
> 18:09:55.356727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [INIT]
> [init tag: 32516609] [rwnd: 102400] [OS: 16] [MIS: 16] [init TSN: 0]
> 18:09:55.356811 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [INIT ACK]
> [init tag: 3168861995] [rwnd: 131072] [OS: 10] [MIS: 16] [init TSN:
> 1877695021]
> 18:09:55.357727 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [COOKIE ECHO]
> 18:09:55.357788 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [COOKIE ACK]
> 18:09:55.358724 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
> 18:09:55.358740 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
> 18:09:55.379715 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [DATA]
> (B)(E) [TSN: 0] [SID: 0] [SSEQ 0] [PPID 0x3]
> 18:09:55.379735 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [SACK]
> [cum ack 0] [a_rwnd 131064] [#gap acks 0] [#dup tsns 0]
> 18:09:55.657716 IP 12.1.1.1.2905 > 11.1.1.11.2905: sctp (1) [HB REQ]
> 18:09:55.657732 IP 11.1.1.11.2905 > 12.1.1.1.2905: sctp (1) [HB ACK]
>
> From the observations, it seems that the LKSCTP library is not able to
> use the original local address when multi-homing is being used. Is
> there anyway can be resolved it?
>
> Thanks
>
> PS