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SubjectRe: tcp timestamp issues with google servers
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On Thu, 2012-05-17 at 11:39 +0200, Miklos Szeredi wrote:
> Sometimes connection to google.com, gmail.com and other google servers
> doesn't work or takes ages to connect. When this hits it hits all
> google servers at the same time and it's persistent. It never happens
> to anything other than google. Rebooting helps. Rarely it goes away
> spontaneously.
>
> Apparently google is sometimes replying with an invalid TSecr timestamp
> value (smaller than the one sent in the last packet) and this confuses
> the Linux TCP stack which either discards the packet or sends a Reset.
>
> Network dump attached.
>
> I found only a couple of references to this issue:
>
> http://gotchas.livejournal.com/3028.html
>
> http://groups.google.com/group/comp.os.linux.networking/browse_thread/thread/29f56feded11b42a
>
> Turning tcp timestamps fixes the issue:
>
> sysctl -w net.ipv4.tcp_timestamps=0
>
> Not sure why this happens only to me and a very few others.
>
> It appears to be an issue with google TCP stack (is it a modified
> stack?) but I thought about issues in my network switch (restarting it
> doesn't help) or something in the ISP, but those look unlikely.
>
> Any ideas?
>
> Thanks,
> Miklos
>
>
>
> 1 0.000000 192.168.28.100 -> 74.125.232.226 TCP 51303 > http [SYN] Seq=0 Win=14600 Len=0 MSS=1460 SACK_PERM=1 TSV=35355050 TSER=0 WS=5
> 2 0.002730 74.125.232.226 -> 192.168.28.100 TCP http > 51303 [SYN, ACK] Seq=0 Ack=1 Win=14180 Len=0 MSS=1430 SACK_PERM=1 TSV=1184565067 TSER=35325344 WS=6


Do you really have 2730 usec RTT between you and this (Google ?)
server ?

Are you sure this is not a broken middle box ?





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