Messages in this thread | | | From | David Brownell <> | Subject | Re: 2.6.11-rc2 TCP ignores PMTU ICMP (Re: Linux 2.6.11-rc2) | Date | Thu, 27 Jan 2005 11:28:48 -0800 |
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On Thursday 27 January 2005 1:02 am, Janos Farkas wrote: > On 2005-01-25 at 10:54:36, David Brownell wrote: > > On Tuesday 25 January 2005 10:35 am, David Ford wrote: > > > PMTU bug -- or better said, bad firewall admin who blocks all ICMP. > > > > PMTU bug, sure -- but one that came late in RC2. Remember: same firewall > > in both cases, but only RC2 breaks. The ICMP packet has landed in > > the RC2 system, which ignores it. 2.6.10 handled it correctly... I > > suspect one of the TCP cleanups borked this.
And in fact, I'm pretty sure RC1 handled it fine too. This failure appeared in a BK pull I did a couple days before RC2, and installing it clobbered a "more virgin" RC1 install; so it's hard to verify.
It took a while to track the failure mode down to being PMTU related, but the only TCP-related changes I noticed in what I pulled sure seemed like cleanups (removing some "duplicated" state).
> > My current workaround is "ifconfig eth0 mtu 1492" but that's not > > something I'd expect to keep. > > Indeed, I had to shuffle my machines around a bit to get a proof that > something is broken, but now I can confirm the above with a connection > to cvs.sourceforge.net:
Thanks for confirming it wasn't just me ... I confess I'm a bit surprised more folk haven't reported this yet!
Your symptoms are exactly like those I saw, just with a different mission-critical application: CVS, not SMTP. Did you happen to notice whether CVS pulls worked, when pushes (like this) failed?
- Dave
> ... > > (the PPPoE gateway notifies the host about the PMTU issue, one for each > segment) > > 08:05:45.265330 IP (tos 0xc0, ttl 128, id 17970, offset 0, flags [none], length: 576) 192.168.59.1 > 192.168.59.10: icmp 556: 66.35.250.207 unreachable - need to frag (mtu 1492) > 08:05:45.265453 IP (tos 0xc0, ttl 128, id 17971, offset 0, flags [none], length: 576) 192.168.59.1 > 192.168.59.10: icmp 556: 66.35.250.207 unreachable - need to frag (mtu 1492) > > (the source host sends the full frame again...?) > > 08:05:45.770331 IP (tos 0x0, ttl 64, id 21544, offset 0, flags [DF], length: 1500) 192.168.59.10.29612 > 66.35.250.207.2401: . [tcp sum ok] 499:1947(1448) ack 526 win 1728 <nop,nop,timestamp 2709754 312383166> > 08:05:45.770900 IP (tos 0xc0, ttl 128, id 17972, offset 0, flags [none], length: 576) 192.168.59.1 > 192.168.59.10: icmp 556: 66.35.250.207 unreachable - need to frag (mtu 1492) > > (and looping goes on..) > > 08:05:46.783148 IP (tos 0x0, ttl 64, id 21546, offset 0, flags [DF], length: 1500) 192.168.59.10.29612 > 66.35.250.207.2401: . [tcp sum ok] 499:1947(1448) ack 526 win 1728 <nop,nop,timestamp 2710768 312383166> > 08:05:46.783752 IP (tos 0xc0, ttl 128, id 17973, offset 0, flags [none], length: 576) 192.168.59.1 > 192.168.59.10: icmp 556: 66.35.250.207 unreachable - need to frag (mtu 1492) > 08:05:48.808861 IP (tos 0x0, ttl 64, id 21548, offset 0, flags [DF], length: 1500) 192.168.59.10.29612 > 66.35.250.207.2401: . [tcp sum ok] 499:1947(1448) ack 526 win 1728 <nop,nop,timestamp 2712796 312383166> > 08:05:48.809882 IP (tos 0xc0, ttl 128, id 17974, offset 0, flags [none], length: 576) 192.168.59.1 > 192.168.59.10: icmp 556: 66.35.250.207 unreachable - need to frag (mtu 1492) > > ... > - 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/
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