Groups > comp.os.linux.networking > #286

Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised

From	Andy Furniss <spam@andyfurniss.entadsl.com>
Newsgroups	comp.os.linux.networking, comp.protocols.tcp-ip
Subject	Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised
Date	2011-05-22 11:40 +0100
Organization	UK Free Software Network
Message-ID	<irap5q$qnu$1@localhost.localdomain> (permalink)
References	(1 earlier) <ir96q3$565$1@dont-email.me> <slrnitgf58.gtj.grahn+nntp@frailea.sa.invalid> <ir9o2p$rcu$1@dont-email.me> <slrnith9la.gtj.grahn+nntp@frailea.sa.invalid> <iradu8$nho$1@dont-email.me>

Cross-posted to 2 groups.

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Mark Hobley wrote:
> On Sun, 22 May 2011 06:01:14 +0000, Jorgen Grahn wrote:
>
>> And then you have GTP tunneling between the routers (SGSN, GGSN) in the
>> 3G network. These frequently pull stupid stunts, too.
>>
>> I don't know ... you also seem to say that IP fragmentation doesn't work
>> for you.  That's so abnormal that perhaps you should debug that first.
>
> I'm trying :)
> What is also weird is that my system has been working with previous kernel
> versions. It has only just become broken again.
>
> I'll try dropping another 12 bytes off the ip route command and retest:
>
> ip route change default via 10.0.0.1 mtu lock 1400
>
> Am I right in that the below datagram is wrong, because the mss is 1460,
> which is above the value of the mtu in the routing table? Shouldn't the
> value of the mtu have been factored in here, and a new mss calculated based
> on the mtu?
>
> 03:43:04.320740 IP venus.markhobley.yi.org.52201>
>> news.eternal-september.org.nntp: Flags [S], seq 2304145392, win 14600,
>> options [mss 1460,sackOK,TS val 47122576 ecr 0,nop,wscale 5], length 0
>

I see the same, but don't know what the behavior should be.
If you set mtu on say eth0 then advertised tcp mss will be affected 
(which in a way is setting mtu plus mru for tcp) - maybe the route 
setting really just does mtu alone, which in a way is what you asked for 
- don't send >1400.

If you want to fix up your wan use iptables mss clamping on the gateway 
if you can.

Using ping to try and work out isp behavior can be misleading - you may 
just be seeing the settings of the server/network you are pinging and 
the pings may get fragged/re-assembled without you knowing.

Thread

Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Mark Hobley <markhobley@yahoo.donottypethisbit.co> - 2011-05-21 14:58 +0000
  Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised "David W. Hodgins" <dwhodgins@nomail.afraid.org> - 2011-05-21 15:16 -0400
    Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-05-21 22:02 +0000
      Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2011-05-22 19:59 +0300
        Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Mark Hobley <markhobley@yahoo.donottypethisbit.co> - 2011-05-22 17:09 +0000
  Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Mark Hobley <markhobley@yahoo.donottypethisbit.co> - 2011-05-21 20:20 +0000
    Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Richard Kettlewell <rjk@greenend.org.uk> - 2011-05-21 22:47 +0100
    Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-05-21 22:28 +0000
      Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Mark Hobley <markhobley@yahoo.donottypethisbit.co> - 2011-05-22 01:15 +0000
        Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-05-22 06:01 +0000
          Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Mark Hobley <markhobley@yahoo.donottypethisbit.co> - 2011-05-22 07:28 +0000
            Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Andy Furniss <spam@andyfurniss.entadsl.com> - 2011-05-22 11:40 +0100
              Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Mark Hobley <markhobley@yahoo.donottypethisbit.co> - 2011-05-22 12:25 +0000
                Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Andy Furniss <spam@andyfurniss.entadsl.com> - 2011-05-22 20:40 +0100
                Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Andy Furniss <spam@andyfurniss.entadsl.com> - 2011-05-22 20:56 +0100
                Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Mark Hobley <markhobley@yahoo.donottypethisbit.co> - 2011-05-22 22:57 +0000
                Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Mark Hobley <markhobley@yahoo.donottypethisbit.co> - 2011-05-22 23:12 +0000
            Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-05-22 11:31 +0000
              Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Mark Hobley <markhobley@yahoo.donottypethisbit.co> - 2011-05-22 11:50 +0000
                Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-05-22 12:52 +0000
                Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Mark Hobley <markhobley@yahoo.donottypethisbit.co> - 2011-05-22 13:27 +0000
                Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-05-22 19:19 +0000
                Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Mark Hobley <markhobley@yahoo.donottypethisbit.co> - 2011-05-22 22:12 +0000
                Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Mark Hobley <markhobley@yahoo.donottypethisbit.co> - 2011-05-25 15:55 +0000
                ip route - Wrong Maximum Segment Size being advertised Mark Hobley <markhobley@yahoo.donottypethisbit.co> - 2011-05-25 17:27 +0000
                Re: Linux 2.6.39.1 - Wrong Maximum Segment Size in both directions Mark Hobley <markhobley@yahoo.donottypethisbit.co> - 2011-05-29 00:34 +0000
                Re: Linux 2.6.39.1 - Wrong Maximum Segment Size in both directions Andy Furniss <spam@andyfurniss.entadsl.com> - 2011-05-29 11:11 +0100
                Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Martijn Lievaart <m@rtij.nl.invlalid> - 2011-05-23 08:13 +0200
    Re: Linux 2.6.39-rc7 - Wrong Maximum Segment Size being advertised Barry Margolin <barmar@alum.mit.edu> - 2011-05-22 00:44 -0400

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