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Date: Wed, 12 Mar 2008 23:19:14 -0500 (CDT)
From: Mike Silbersack <silby@silby.com>
To: "d.s. al coda" <coda.trigger@gmail.com>
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Cc: freebsd-net@freebsd.org
Subject: Re: TCP options order changed in FreeBSD 7, incompatible with some
 routers
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On Tue, 11 Mar 2008, d.s. al coda wrote:

> - FreeBSD 7 has <mss 1412, sackOK, eol> (there is of course an aligning nop
> after the eol, which tcpdump skips)

Jake Rizzo sent me some updated tcpdumps comparing 6.3 vs 7.0, and that 
aligning NOP that tcpdump (and wireshark) omit seems to be the only 
difference.

Here's what Jake's 6.3 dump shows:

IP A > B : S 2575736483:2575736483(0) ack 1762868649 win 65535 <mss 1460,sackOK,eol>

And the actual option data is:
02 04 05 b4 04 02 00 00 <- ends with two EOLs

For 7.0:
IP A > B : S 3304309835:3304309835(0) ack 710421411 win 65535 <mss 1380,sackOK,eol>

And the actual option data is:
02 04 05 64 04 02 00 01 <- ends with a NOP after the EOL

I think we will need to fix tcpdump before trying to finish diagnosing 
this problem.  We were missing key information before.

-Mike