Re: ARP routing issue

Re: ARP routing issue

[Zhenyu Wu]

I met a question about ARP. If i send packet to another host using Raw socket at
one host and i set protocol type into TCP, then at another host i receive the
packet, but when i read the field skb->protocol, it is ARP. But when i changed a
host to send the packet, it does well. 

There are something wrong on my network card or the Kernel?


>Hello,
> 
> Have a look at /proc/sys/net/conf/XXX/arp_filter :
> 
>         
> arp_filter - BOOLEAN
>         1 - Allows you to have multiple network interfaces on the same
>         subnet, and have the ARPs for each interface be answered
>         based on whether or not the kernel would route a packet from
>         the ARP'd IP out that interface (therefore you must use source
>         based routing for this to work). In other words it allows control
>         of which cards (usually 1) will respond to an arp request.
> 
>         0 - (default) The kernel can respond to arp requests with addresses
>         from other interfaces. This may seem wrong but it usually makes
>         sense, because it increases the chance of successful communication.
>         IP addresses are owned by the complete host on Linux, not by
>         particular interfaces. Only for more complex setups like load-
>         balancing, does this behaviour cause problems.
> 
> Regards,
> Paul
> 
> Paul Rolland, rol(at)as2917.net
> ex-AS2917 Network administrator and Peering Coordinator
> 
> --
> 
> Please no HTML, I'm not a browser - Pas d'HTML, je ne suis pas un navigateur
> 
> "Some people dream of success... while others wake up and work hard at it" 
> 
>   
> 
> > -----Message d'origine-----
> > De : linux-kernel-owner@vger.kernel.org 
> > [mailto:linux-kernel-owner@vger.kernel.org] De la part de Jan De Luyck
> > Envoy?: jeudi 6 janvier 2005 17:12
> > ?: Steve Iribarne
> > Cc : linux-kernel@vger.kernel.org; linux-net@vger.kernel.org
> > Objet : Re: ARP routing issue
> > 
> > On Thursday 06 January 2005 17:06, Steve Iribarne wrote:
> > > Hi Jan,
> > >
> > >
> > > -> default gateway is set to 10.0.22.1, on eth0.
> > > ->
> > > -> Problem is, if I try to ping from another network
> > > -> (10.216.0.xx) to 10.0.24.xx, i see the following ARP request:
> > > ->
> > > -> arp who-has 10.0.22.1 tell 10.0.24.xx
> > > ->
> > >
> > > You see that coming out the eth0 interface??
> > >
> > > If that is the case it is most definately wrong.  Assuming that your
> > > masks are setup properly.  But I haven't worked on the 2.4 
> > kernel for a
> > > long time so I'm not so sure if what you are seeing is a 
> > bug that has
> > > been fixed.
> > 
> > The network information is:
> > eth0 10.0.22.xxx mask 255.255.255.0
> > eth1 10.0.24.xxx mask 255.255.255.0
> > 
> > routing:
> > 10.0.22.0 0.0.0.0 255.255.255.0 eth0
> > 10.0.24.0 0.0.0.0 255.255.255.0 eth1
> > 0.0.0.0  10.0.22.1 0.0.0.0  eth0
> > 
> > Jan
> > 
> > -- 
> > If a man slept by day, he had little time to work.  That was a
> > satisfying notion to Escargot.
> >   -- "The Stone Giant", James P. Blaylock
> > -
> > To unsubscribe from this list: send the line "unsubscribe 
> > linux-kernel" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at  http://www.tux.org/lkml/
> > 
> 
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
>

Re: ARP routing issue

[Alan Cox]

On Sad, 2005-01-15 at 12:31, Jan De Luyck wrote:
> On Friday 14 January 2005 23:47, James Courtier-Dutton wrote:
> > That arp is perfectly OK.
> > The routing table will cause the icmp echo packet to go from 10.216.0.xx
> > to 10.0.24.xx via the 10.0.24.x network.
> > The icmp echo response will return via the 10.0.22.x network back to the
> > 10.216.0.xx network.
> > So the paths in each direction are different.
> 
> Yes, but unfortunately I never ever receive the icmp echo reply, and the arp 
> table always lists the ip as "incomplete". Nothing I try to do to with that 
> interface (ssh/...) ever works.

If the directions are different does your distro enable rp_filter by
default - that may cause such problems. You might also want to ask on
netdev@oss.sgi.com - the network layer list

Re: ARP routing issue

[Jan De Luyck]

On Friday 14 January 2005 23:47, James Courtier-Dutton wrote:
> That arp is perfectly OK.
> The routing table will cause the icmp echo packet to go from 10.216.0.xx
> to 10.0.24.xx via the 10.0.24.x network.
> The icmp echo response will return via the 10.0.22.x network back to the
> 10.216.0.xx network.
> So the paths in each direction are different.

Yes, but unfortunately I never ever receive the icmp echo reply, and the arp 
table always lists the ip as "incomplete". Nothing I try to do to with that 
interface (ssh/...) ever works.

Jan

-- 
Real Programmers don't eat quiche.  They eat Twinkies and Szechwan food.

Re: ARP routing issue

[James Courtier-Dutton]

Jan De Luyck wrote:
> On Thursday 06 January 2005 17:06, Steve Iribarne wrote:
> 
>>Hi Jan,
>>
>>
>>-> default gateway is set to 10.0.22.1, on eth0.
>>->
>>-> Problem is, if I try to ping from another network
>>-> (10.216.0.xx) to 10.0.24.xx, i see the following ARP request:
>>->
>>-> arp who-has 10.0.22.1 tell 10.0.24.xx
>>->
>>
>>You see that coming out the eth0 interface??
>>
>>If that is the case it is most definately wrong.  Assuming that your
>>masks are setup properly.  But I haven't worked on the 2.4 kernel for a
>>long time so I'm not so sure if what you are seeing is a bug that has
>>been fixed.
> 
> 
> The network information is:
> eth0 10.0.22.xxx mask 255.255.255.0
> eth1 10.0.24.xxx mask 255.255.255.0
> 
> routing:
> 10.0.22.0 0.0.0.0 255.255.255.0 eth0
> 10.0.24.0 0.0.0.0 255.255.255.0 eth1
> 0.0.0.0  10.0.22.1 0.0.0.0  eth0
> 
> Jan
> 

That arp is perfectly OK.
The routing table will cause the icmp echo packet to go from 10.216.0.xx 
to 10.0.24.xx via the 10.0.24.x network.
The icmp echo response will return via the 10.0.22.x network back to the 
10.216.0.xx network.
So the paths in each direction are different.

the "arp who-has 10.0.22.1 tell 10.0.24.xx", you can safely ignore the 
"10.0.24.xx" bit, as that will be ignored by the device responding to 
the ARP.
It is just highlighting the point that you have 2 paths to the same 
destination.

Cheers

James

Re: ARP routing issue

[Jan De Luyck]

On Friday 07 January 2005 08:44, Julian Anastasov wrote:
>  Hello,
>
> On Thu, 6 Jan 2005, Jan De Luyck wrote:
> > http://www.uwsg.iu.edu/hypermail/linux/net/0308.1/0071.html
> >
> > Basically it comes down to this:
> >
> > I have an IBM server running RH ES, kernel 2.4.9-e.49. It has two
> > interfaces: eth0 10.0.22.xxx
> > eth1 10.0.24.xxx
> >
> > default gateway is set to 10.0.22.1, on eth0.
> >
> > Problem is, if I try to ping from another network (10.216.0.xx) to
> > 10.0.24.xx, i see the following ARP request:
> >
> > arp who-has 10.0.22.1 tell 10.0.24.xx
> >
> > which, imo, is wrong.
> >
> > I know it has to do with the default gatway, but I can't devise a way to
> > make it actually _WORK_.
>
>  Not wrong but it is one of the possible valid requests. 

Yes, I've gathered that. Yet, it seems very strange, and I want to _change_ 
that behaviour.

>  If it 
> is ignored from other boxes in your setup then you can look
> at new kernels. 2.4.26 and 2.6.4 come with new sysctl flags for ARP.
> arp_filter filters incoming requests but you can use arp_announce to
> control the source IP when sending requests, eg. in IBM server you can set
> /proc/sys/net/ipv4/conf/eth*/arp_announce to 1 or 2 or even just
> /proc/sys/net/ipv4/conf/all/arp_announce to 1 or 2

Hmm. Point is, for certification/support reasons we'd rather stick to the 
RedHat ES supplied kernels instead of starting off with one of our own. I 
can't go off running non-checked-to-be-stable (in a business POV) code on 
mission-critical systems. (2.6.10 is stable enough in _my_ POV, but well..)

Jan

-- 
Serfs up!
  -- Spartacus

Re: ARP routing issue

[Julian Anastasov]

	Hello,

On Thu, 6 Jan 2005, Jan De Luyck wrote:

> http://www.uwsg.iu.edu/hypermail/linux/net/0308.1/0071.html
>
> Basically it comes down to this:
>
> I have an IBM server running RH ES, kernel 2.4.9-e.49. It has two interfaces:
> eth0 10.0.22.xxx
> eth1 10.0.24.xxx
>
> default gateway is set to 10.0.22.1, on eth0.
>
> Problem is, if I try to ping from another network (10.216.0.xx) to 10.0.24.xx,
> i see the following ARP request:
>
> arp who-has 10.0.22.1 tell 10.0.24.xx
>
> which, imo, is wrong.
>
> I know it has to do with the default gatway, but I can't devise a way to make
> it actually _WORK_.

	Not wrong but it is one of the possible valid requests. If it
is ignored from other boxes in your setup then you can look 
at new kernels. 2.4.26 and 2.6.4 come with new sysctl flags for ARP. 
arp_filter filters incoming requests but you can use arp_announce to 
control the source IP when sending requests, eg. in IBM server you can set
/proc/sys/net/ipv4/conf/eth*/arp_announce to 1 or 2 or even just
/proc/sys/net/ipv4/conf/all/arp_announce to 1 or 2

> Any pointers?

See Documentation/networking/ip-sysctl.txt for more info.

> Thanks.
>
> Jan

Regards

--
Julian Anastasov <ja@ssi.bg>

Re: ARP routing issue

[Jan De Luyck]

[-- Attachment #1: Type: text/plain, Size: 2070 bytes --]

On Thursday 06 January 2005 18:51, Alan Cox wrote:
> On Iau, 2005-01-06 at 15:47, Jan De Luyck wrote:
> > Problem is, if I try to ping from another network (10.216.0.xx) to
> > 10.0.24.xx, i see the following ARP request:
> >
> > arp who-has 10.0.22.1 tell 10.0.24.xx
> >
> > which, imo, is wrong.
>
> With the info you've given it could be right or wrong. Can you provide a
> mini plumbing diagram to go with it. Who is arping for what too ?

Hello Alan,

Here's the plumbing schematic, in ASCII. For readability sake i've also included a png image.

--------------- 10.0.22.0 / 255.255.255.0 -----------------|
           |                                               |
   eth0    |    10.0.22.x                                  |
  ------------------------                                 |
  | IBM Server           |                                 |
  ------------------------                                 |
   eth1    | 10.0.24.x                                     |
           |                                               |
--------------- 10.0.24.x / 255.255.255.0 -----------|     |
                                                     |     |
                                          10.0.24.1  |     |  10.0.22.1
                                            --------------------------
                                            | CISCO Switching router |
                                            --------------------------
                                                     |
                                                     |
           ---------- 10.216.0.0 / 255.255.0.0 ----------------
                                                   |
                                                   | 10.216.x.x
                                           ------------------
                                           | Client station |
                                           ------------------

I am pinging (icmp ping) from client station to eth1 of the server.

Jan
-- 
Q: What do you call a boomerang that doesn't come back?
A: A stick.

[-- Attachment #2: arp_problem.png --]
[-- Type: image/png, Size: 14667 bytes --]

Re: ARP routing issue

[Jan De Luyck]

On Thursday 06 January 2005 18:53, Paul Rolland wrote:
> Hello,
>
> Have a look at /proc/sys/net/conf/XXX/arp_filter :
>
>
> arp_filter - BOOLEAN
>         1 - Allows you to have multiple network interfaces on the same
>         subnet, and have the ARPs for each interface be answered
>         based on whether or not the kernel would route a packet from
>         the ARP'd IP out that interface (therefore you must use source
>         based routing for this to work). In other words it allows control
>         of which cards (usually 1) will respond to an arp request.
>
>         0 - (default) The kernel can respond to arp requests with addresses
>         from other interfaces. This may seem wrong but it usually makes
>         sense, because it increases the chance of successful communication.
>         IP addresses are owned by the complete host on Linux, not by
>         particular interfaces. Only for more complex setups like load-
>         balancing, does this behaviour cause problems.
>
> Regards,
> Paul

I tried that actually, didn't change a thing.

Jan

-- 
Beware of computerized fortune-tellers!

Re: ARP routing issue

[Jan De Luyck]

On Thursday 06 January 2005 18:51, Steve Iribarne wrote:
> And you see the arp packet coming out which interface??
>

eth0

Jan
-- 
If we all work together, we can totally disrupt the system.

Re: ARP routing issue

[Paul Rolland]

Hello,

Have a look at /proc/sys/net/conf/XXX/arp_filter :

        
arp_filter - BOOLEAN
        1 - Allows you to have multiple network interfaces on the same
        subnet, and have the ARPs for each interface be answered
        based on whether or not the kernel would route a packet from
        the ARP'd IP out that interface (therefore you must use source
        based routing for this to work). In other words it allows control
        of which cards (usually 1) will respond to an arp request.

        0 - (default) The kernel can respond to arp requests with addresses
        from other interfaces. This may seem wrong but it usually makes
        sense, because it increases the chance of successful communication.
        IP addresses are owned by the complete host on Linux, not by
        particular interfaces. Only for more complex setups like load-
        balancing, does this behaviour cause problems.

Regards,
Paul

Paul Rolland, rol(at)as2917.net
ex-AS2917 Network administrator and Peering Coordinator

--

Please no HTML, I'm not a browser - Pas d'HTML, je ne suis pas un navigateur

"Some people dream of success... while others wake up and work hard at it" 

  

> -----Message d'origine-----
> De : linux-kernel-owner@vger.kernel.org 
> [mailto:linux-kernel-owner@vger.kernel.org] De la part de Jan De Luyck
> Envoyé : jeudi 6 janvier 2005 17:12
> À : Steve Iribarne
> Cc : linux-kernel@vger.kernel.org; linux-net@vger.kernel.org
> Objet : Re: ARP routing issue
> 
> On Thursday 06 January 2005 17:06, Steve Iribarne wrote:
> > Hi Jan,
> >
> >
> > -> default gateway is set to 10.0.22.1, on eth0.
> > ->
> > -> Problem is, if I try to ping from another network
> > -> (10.216.0.xx) to 10.0.24.xx, i see the following ARP request:
> > ->
> > -> arp who-has 10.0.22.1 tell 10.0.24.xx
> > ->
> >
> > You see that coming out the eth0 interface??
> >
> > If that is the case it is most definately wrong.  Assuming that your
> > masks are setup properly.  But I haven't worked on the 2.4 
> kernel for a
> > long time so I'm not so sure if what you are seeing is a 
> bug that has
> > been fixed.
> 
> The network information is:
> eth0 10.0.22.xxx mask 255.255.255.0
> eth1 10.0.24.xxx mask 255.255.255.0
> 
> routing:
> 10.0.22.0 0.0.0.0 255.255.255.0 eth0
> 10.0.24.0 0.0.0.0 255.255.255.0 eth1
> 0.0.0.0  10.0.22.1 0.0.0.0  eth0
> 
> Jan
> 
> -- 
> If a man slept by day, he had little time to work.  That was a
> satisfying notion to Escargot.
>   -- "The Stone Giant", James P. Blaylock
> -
> To unsubscribe from this list: send the line "unsubscribe 
> linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
> 

RE: ARP routing issue

[Steve Iribarne]

And you see the arp packet coming out which interface??

 

-> -----Original Message-----
-> From: Jan De Luyck [mailto:lkml@kcore.org] 
-> Sent: Thursday, January 06, 2005 8:12 AM
-> To: Steve Iribarne
-> Cc: linux-kernel@vger.kernel.org; linux-net@vger.kernel.org
-> Subject: Re: ARP routing issue
-> 
-> On Thursday 06 January 2005 17:06, Steve Iribarne wrote:
-> > Hi Jan,
-> >
-> >
-> > -> default gateway is set to 10.0.22.1, on eth0.
-> > ->
-> > -> Problem is, if I try to ping from another network
-> > -> (10.216.0.xx) to 10.0.24.xx, i see the following ARP request:
-> > ->
-> > -> arp who-has 10.0.22.1 tell 10.0.24.xx
-> > ->
-> >
-> > You see that coming out the eth0 interface??
-> >
-> > If that is the case it is most definately wrong.  Assuming 
-> that your 
-> > masks are setup properly.  But I haven't worked on the 2.4 
-> kernel for 
-> > a long time so I'm not so sure if what you are seeing is a 
-> bug that 
-> > has been fixed.
-> 
-> The network information is:
-> eth0 10.0.22.xxx mask 255.255.255.0
-> eth1 10.0.24.xxx mask 255.255.255.0
-> 
-> routing:
-> 10.0.22.0 0.0.0.0 255.255.255.0 eth0
-> 10.0.24.0 0.0.0.0 255.255.255.0 eth1
-> 0.0.0.0  10.0.22.1 0.0.0.0  eth0
-> 
-> Jan
-> 
-> --
-> If a man slept by day, he had little time to work.  That was 
-> a satisfying notion to Escargot.
->   -- "The Stone Giant", James P. Blaylock
-> 

Re: ARP routing issue

[Alan Cox]

On Iau, 2005-01-06 at 15:47, Jan De Luyck wrote:
> Problem is, if I try to ping from another network (10.216.0.xx) to 10.0.24.xx, 
> i see the following ARP request:
> 
> arp who-has 10.0.22.1 tell 10.0.24.xx
> 
> which, imo, is wrong.

With the info you've given it could be right or wrong. Can you provide a
mini plumbing diagram to go with it. Who is arping for what too ?

Re: ARP routing issue

[Jan De Luyck]

On Thursday 06 January 2005 17:06, Steve Iribarne wrote:
> Hi Jan,
>
>
> -> default gateway is set to 10.0.22.1, on eth0.
> ->
> -> Problem is, if I try to ping from another network
> -> (10.216.0.xx) to 10.0.24.xx, i see the following ARP request:
> ->
> -> arp who-has 10.0.22.1 tell 10.0.24.xx
> ->
>
> You see that coming out the eth0 interface??
>
> If that is the case it is most definately wrong.  Assuming that your
> masks are setup properly.  But I haven't worked on the 2.4 kernel for a
> long time so I'm not so sure if what you are seeing is a bug that has
> been fixed.

The network information is:
eth0 10.0.22.xxx mask 255.255.255.0
eth1 10.0.24.xxx mask 255.255.255.0

routing:
10.0.22.0 0.0.0.0 255.255.255.0 eth0
10.0.24.0 0.0.0.0 255.255.255.0 eth1
0.0.0.0  10.0.22.1 0.0.0.0  eth0

Jan

-- 
If a man slept by day, he had little time to work.  That was a
satisfying notion to Escargot.
  -- "The Stone Giant", James P. Blaylock

RE: ARP routing issue

[Steve Iribarne]

Hi Jan,

 
-> default gateway is set to 10.0.22.1, on eth0.
-> 
-> Problem is, if I try to ping from another network 
-> (10.216.0.xx) to 10.0.24.xx, i see the following ARP request:
-> 
-> arp who-has 10.0.22.1 tell 10.0.24.xx
->

You see that coming out the eth0 interface??  

If that is the case it is most definately wrong.  Assuming that your
masks are setup properly.  But I haven't worked on the 2.4 kernel for a
long time so I'm not so sure if what you are seeing is a bug that has
been fixed.

-stv

ARP routing issue

[Jan De Luyck]

Hello lists,

Sorry to bother you with this probably beat-to-death issue, but I can't figure 
out the solution to the problem.

It's perfectly described in this archive thread:

http://www.uwsg.iu.edu/hypermail/linux/net/0308.1/0071.html

Basically it comes down to this:

I have an IBM server running RH ES, kernel 2.4.9-e.49. It has two interfaces:
eth0 10.0.22.xxx 
eth1 10.0.24.xxx

default gateway is set to 10.0.22.1, on eth0.

Problem is, if I try to ping from another network (10.216.0.xx) to 10.0.24.xx, 
i see the following ARP request:

arp who-has 10.0.22.1 tell 10.0.24.xx

which, imo, is wrong.

I know it has to do with the default gatway, but I can't devise a way to make 
it actually _WORK_.

Any pointers?

Thanks.

Jan
-- 
No one can feel as helpless as the owner of a sick goldfish.