TCP options order changed in FreeBSD 7, incompatible with some
routers
Mike Silbersack
silby at silby.com
Wed Mar 12 21:19:17 PDT 2008
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
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