* possible routing table cache bug for mtu/advmss attributes in Linux 3.0.4
@ 2011-09-02 12:34 David Madore
0 siblings, 0 replies; 4+ messages in thread
From: David Madore @ 2011-09-02 12:34 UTC (permalink / raw)
To: Linux Kernel Mailing-List
Hi,
I believe I've found a bug in the routing cache (perhaps only for
IPv6) in Linux 3.0.4. Since I'm uncertain about the diagnosis, I'm
posting here for guidance as to how to proceed.
In a nutshell, the problem is this: my (manually entered) routing
tables specify an explicit MTU/MSS for certain IPv6 routes, and after
upgrading from 2.6.38.7 to 3.0.4, I found that this MTU/MSS setting is
sometimes ignored. More precisely, it seems that connecting to a host
through the route in question causes a routing cache entry to be
created, and it is when this cache entry expires that the route
forgets the MTU/MSS setting. (It may also be relevant that in my case
the route belongs to a routing table other than "main".)
In more details: my routing tables contains the following:
vega david ~ $ sudo ip -6 rule show
0: from all lookup local
32766: from all lookup main
40000: from 2002::/16 lookup 2002
40100: from all lookup 2001
vega david ~ $ sudo ip -6 route show table 2001
2002::/16 via ::192.88.99.1 dev tun6to4 metric 512 mtu 1466 advmss 1406
2000::/3 dev ppp0 metric 64 mtu 1466 advmss 1406
Initially, trying to get the route to 2001:41d0:1:a431::1 correctly
returns route with the mtu and advmss values I entered:
vega david ~ $ sudo ip route get 2001:41d0:1:a431::1
2001:41d0:1:a431::1 from :: via 2001:41d0:1:a431::1 dev ppp0 src 2001:7a8:78ae::1 metric 0
cache mtu 1466 advmss 1406
Now I start an ssh connection to 2001:41d0:1:a431::1, close it
immediately, and fetch the route again:
vega david ~ $ sudo ip route get 2001:41d0:1:a431::1
2001:41d0:1:a431::1 from :: via 2001:41d0:1:a431::1 dev ppp0 src 2001:7a8:78ae::1 metric 0
cache mtu 1466 rtt 37ms rttvar 37ms cwnd 10 advmss 1406
This is still correct. But if I wait a few seconds (doing nothing)
for these data to expire, they seems to take the mtu and advmss values
away with them:
vega david ~ $ sudo ip route get 2001:41d0:1:a431::1
2001:41d0:1:a431::1 from :: via 2001:41d0:1:a431::1 dev ppp0 src 2001:7a8:78ae::1 metric 0
cache
(note the empty "cache" line and the absence of mtu/advmss settings).
This is not just wrongly reported: the route really is wrong, and
opening a TCP connection at this stage will use a wrong MSS (and
freeze on large packets, because my Internet provider is worthless,
but that's another story). At some point the route seems to return to
normal, but I couldn't figure out what causes this exactly.
In case it's uesful, my kernel config is on <URL:
http://www.madore.org/~david/.tmp/config-3.0.4-vega
>.
Any thoughts?
--
David A. Madore
( http://www.madore.org/~david/ )
^ permalink raw reply [flat|nested] 4+ messages in thread
* possible routing table cache bug for mtu/advmss attributes in Linux 3.0.4
@ 2011-09-01 21:46 David Madore
2011-09-08 14:42 ` Yan, Zheng
0 siblings, 1 reply; 4+ messages in thread
From: David Madore @ 2011-09-01 21:46 UTC (permalink / raw)
To: Linux Netdev Mailing-List
Hi,
I believe I've found a bug in the routing cache (perhaps only for
IPv6) in Linux 3.0.4. Since I'm uncertain about the diagnosis, I'm
posting here for guidance as to how to proceed.
In a nutshell, the problem is this: my (manually entered) routing
tables specify an explicit MTU/MSS for certain IPv6 routes, and after
upgrading from 2.6.38.7 to 3.0.4, I found that this MTU/MSS setting is
sometimes ignored. More precisely, it seems that connecting to a host
through the route in question causes a routing cache entry to be
created, and it is when this cache entry expires that the route
forgets the MTU/MSS setting. (It may also be relevant that in my case
the route belongs to a routing table other than "main".)
In more details: my routing tables contains the following:
vega david ~ $ sudo ip -6 rule show
0: from all lookup local
32766: from all lookup main
40000: from 2002::/16 lookup 2002
40100: from all lookup 2001
vega david ~ $ sudo ip -6 route show table 2001
2002::/16 via ::192.88.99.1 dev tun6to4 metric 512 mtu 1466 advmss 1406
2000::/3 dev ppp0 metric 64 mtu 1466 advmss 1406
Initially, trying to get the route to 2001:41d0:1:a431::1 correctly
returns route with the mtu and advmss values I entered:
vega david ~ $ sudo ip route get 2001:41d0:1:a431::1
2001:41d0:1:a431::1 from :: via 2001:41d0:1:a431::1 dev ppp0 src 2001:7a8:78ae::1 metric 0
cache mtu 1466 advmss 1406
Now I start an ssh connection to 2001:41d0:1:a431::1, close it
immediately, and fetch the route again:
vega david ~ $ sudo ip route get 2001:41d0:1:a431::1
2001:41d0:1:a431::1 from :: via 2001:41d0:1:a431::1 dev ppp0 src 2001:7a8:78ae::1 metric 0
cache mtu 1466 rtt 37ms rttvar 37ms cwnd 10 advmss 1406
This is still correct. But if I wait a few seconds (doing nothing)
for these data to expire, they seems to take the mtu and advmss values
away with them:
vega david ~ $ sudo ip route get 2001:41d0:1:a431::1
2001:41d0:1:a431::1 from :: via 2001:41d0:1:a431::1 dev ppp0 src 2001:7a8:78ae::1 metric 0
cache
(note the empty "cache" line and the absence of mtu/advmss settings).
This is not just wrongly reported: the route really is wrong, and
opening a TCP connection at this stage will use a wrong MSS (and
freeze on large packets, because my Internet provider is worthless,
but that's another story). At some point the route seems to return to
normal, but I couldn't figure out what causes this exactly.
In case it's uesful, my kernel config is on <URL:
http://www.madore.org/~david/.tmp/config-3.0.4-vega
>.
Any thoughts?
--
David A. Madore
( http://www.madore.org/~david/ )
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: possible routing table cache bug for mtu/advmss attributes in Linux 3.0.4
2011-09-01 21:46 David Madore
@ 2011-09-08 14:42 ` Yan, Zheng
2011-09-09 21:28 ` David Madore
0 siblings, 1 reply; 4+ messages in thread
From: Yan, Zheng @ 2011-09-08 14:42 UTC (permalink / raw)
To: David Madore; +Cc: Linux Netdev Mailing-List
On Fri, Sep 2, 2011 at 5:46 AM, David Madore <david+ml@madore.org> wrote:
> Hi,
>
> I believe I've found a bug in the routing cache (perhaps only for
> IPv6) in Linux 3.0.4. Since I'm uncertain about the diagnosis, I'm
> posting here for guidance as to how to proceed.
>
> In a nutshell, the problem is this: my (manually entered) routing
> tables specify an explicit MTU/MSS for certain IPv6 routes, and after
> upgrading from 2.6.38.7 to 3.0.4, I found that this MTU/MSS setting is
> sometimes ignored. More precisely, it seems that connecting to a host
> through the route in question causes a routing cache entry to be
> created, and it is when this cache entry expires that the route
> forgets the MTU/MSS setting. (It may also be relevant that in my case
> the route belongs to a routing table other than "main".)
>
> In more details: my routing tables contains the following:
>
> vega david ~ $ sudo ip -6 rule show
> 0: from all lookup local
> 32766: from all lookup main
> 40000: from 2002::/16 lookup 2002
> 40100: from all lookup 2001
> vega david ~ $ sudo ip -6 route show table 2001
> 2002::/16 via ::192.88.99.1 dev tun6to4 metric 512 mtu 1466 advmss 1406
> 2000::/3 dev ppp0 metric 64 mtu 1466 advmss 1406
>
> Initially, trying to get the route to 2001:41d0:1:a431::1 correctly
> returns route with the mtu and advmss values I entered:
>
> vega david ~ $ sudo ip route get 2001:41d0:1:a431::1
> 2001:41d0:1:a431::1 from :: via 2001:41d0:1:a431::1 dev ppp0 src 2001:7a8:78ae::1 metric 0
> cache mtu 1466 advmss 1406
>
> Now I start an ssh connection to 2001:41d0:1:a431::1, close it
> immediately, and fetch the route again:
>
> vega david ~ $ sudo ip route get 2001:41d0:1:a431::1
> 2001:41d0:1:a431::1 from :: via 2001:41d0:1:a431::1 dev ppp0 src 2001:7a8:78ae::1 metric 0
> cache mtu 1466 rtt 37ms rttvar 37ms cwnd 10 advmss 1406
>
> This is still correct. But if I wait a few seconds (doing nothing)
> for these data to expire, they seems to take the mtu and advmss values
> away with them:
>
> vega david ~ $ sudo ip route get 2001:41d0:1:a431::1
> 2001:41d0:1:a431::1 from :: via 2001:41d0:1:a431::1 dev ppp0 src 2001:7a8:78ae::1 metric 0
> cache
>
> (note the empty "cache" line and the absence of mtu/advmss settings).
>
> This is not just wrongly reported: the route really is wrong, and
> opening a TCP connection at this stage will use a wrong MSS (and
> freeze on large packets, because my Internet provider is worthless,
> but that's another story). At some point the route seems to return to
> normal, but I couldn't figure out what causes this exactly.
>
> In case it's uesful, my kernel config is on <URL:
> http://www.madore.org/~david/.tmp/config-3.0.4-vega
> >.
>
Would you please try patch http://marc.info/?l=linux-netdev&m=131529445904858
Thanks
> Any thoughts?
>
> --
> David A. Madore
> ( http://www.madore.org/~david/ )
> --
> To unsubscribe from this list: send the line "unsubscribe netdev" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: possible routing table cache bug for mtu/advmss attributes in Linux 3.0.4
2011-09-08 14:42 ` Yan, Zheng
@ 2011-09-09 21:28 ` David Madore
0 siblings, 0 replies; 4+ messages in thread
From: David Madore @ 2011-09-09 21:28 UTC (permalink / raw)
To: Yan, Zheng ; +Cc: Linux Netdev Mailing-List
On Thu, Sep 08, 2011 at 10:42:20PM +0800, Yan, Zheng wrote:
> On Fri, Sep 2, 2011 at 5:46 AM, David Madore <david+ml@madore.org> wrote:
> > In a nutshell, the problem is this: my (manually entered) routing
> > tables specify an explicit MTU/MSS for certain IPv6 routes, and after
> > upgrading from 2.6.38.7 to 3.0.4, I found that this MTU/MSS setting is
> > sometimes ignored. More precisely, it seems that connecting to a host
> > through the route in question causes a routing cache entry to be
> > created, and it is when this cache entry expires that the route
> > forgets the MTU/MSS setting. (It may also be relevant that in my case
> > the route belongs to a routing table other than "main".)
>
> Would you please try patch http://marc.info/?l=linux-netdev&m=131529445904858
Indeed, this appears to solve the problem I encountered. Thanks!
--
David A. Madore
( http://www.madore.org/~david/ )
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2011-09-09 21:28 UTC | newest]
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2011-09-01 21:46 David Madore
2011-09-08 14:42 ` Yan, Zheng
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