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Date: Thu, 20 Mar 2003 16:19:12 +0100
From: bert hubert <ahu@ds9a.nl>
To: netdev@oss.sgi.com, linux-kernel@vger.kernel.org
Cc: davem@redhat.com
Subject: [some more data]  Re: [BUG] 2.5.65 ipv6 TCP checksum errors (capture attached)
Message-ID: <20030320151912.GA25487@outpost.ds9a.nl>
Mail-Followup-To: bert hubert <ahu@ds9a.nl>, netdev@oss.sgi.com,
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On Wed, Mar 19, 2003 at 01:45:33PM +0100, bert hubert wrote:
> Interestingly, the initial ssh connection worked, the second one failed.
> Subsequent attempts fail too.

I've since let loose the excellent ethereal on this and found out:

> hubert# tcpdump -r file -v -v
> 29.09 snapcount.33408 > hubert.ssh: S [tcp sum ok] 2737328594:2737328594(0) win 5760 <mss 1440,sackOK,timestamp 10690463 0,nop,wscale 0> (len 40, hlim 64)
> 29.09 hubert.ssh > snapcount.33408: S [tcp sum ok] 2399386333:2399386333(0) ack 2737328595 win 5712 <mss 1440,sackOK,timestamp 10865690 10690463,nop,wscale 0> (len 40, hlim 64)
> 29.09 snapcount.33408 > hubert.ssh: . [tcp sum ok] 1:1(0) ack 1 win 5760 <nop,nop,timestamp 10690464 10865690> (len 32, hlim 64)

So far so good.

> 29.10 hubert.ssh > snapcount.33408: P [bad tcp cksum 4f2!] 1:41(40) ack 1 win 5712 <nop,nop,timestamp 10865695 10690464> (len 72, hlim 64)
> 29.30 hubert.ssh > snapcount.33408: P [bad tcp cksum 3bf1!] 1:41(40) ack 1 win 5712 <nop,nop,timestamp 10865896 10690464> (len 72, hlim 64)
> 29.83 hubert.ssh > snapcount.33408: P [bad tcp cksum 23ef!] 1:41(40) ack 1 win 5712 <nop,nop,timestamp 10866432 10690464> (len 72, hlim 64)
> 30.86 hubert.ssh > snapcount.33408: P [bad tcp cksum 23eb!] 1:41(40) ack 1 win 5712 <nop,nop,timestamp 10867456 10690464> (len 72, hlim 64)

These packets all have an identical csum of 0x680d, it is not being updated.
So, the SYN/SYNACK/ACK stuff went fine, the initial data however has a wrong
checksum. 

For completeness, I've attached the capture again.

Regards,

bert

-- 
http://www.PowerDNS.com      Open source, database driven DNS Software 
http://lartc.org           Linux Advanced Routing & Traffic Control HOWTO
http://netherlabs.nl                         Consulting
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1MOyoQIABAAAAAAAAAAAANwFAAABAAAAiWR4Pht3AQBeAAAAXgAAAAAIoRnw8ACgzMjyXIbd
YAAAAAAoBkAgAQiIEDYAAAIIof/+GfDxIAEIiBA2AAACCKH//hnw8IKAABajKFHSAAAAAKAC
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