Interesting TCP issue

[Steve Watt]

On Jan 1, 23:56, Julian Elischer wrote:
} Subject: Re: Interesting TCP issue
} Steve Watt wrote:
} > One of my users is having trouble receiving mail from Skype.  So,
} > after some sniffing, I discovered this:
} > 
} > # tcpdump -vv -s 1500 -i dc0 -X net 213.244.128.0/18
} > tcpdump: lestening on dc0, link-type EN10MB (Ethernet), capture size 1500 bytes
} > 13:18:13.607493 IP (tos 0x20, ttl  58, id 12896, offset 0, flags [DF], proto: TCP (6), length: 74) share.skype.net.50406 > wattres.watt.com.smtp: P, cksum 0x9297 (correct), 4072464914:4072464936(22) ack 1248591103 win 46 <nop,nop,timestamp 2511885672 520058954>
[ sneck ]
} > 
} > And no responses from my system.
} > 
} > Interesting.  I presume it has something to do with the
} > idiotically small window the remote server is advertising.  So I
} > set net.inet.tcp.minmss down to 46, and that resulted in a RST
} > being spit back to skype's server when its retransmit happened.
} > [...]
} 
} turn off window scaling (I forget the sysctl) and see if that helps
} It's broken in some versions of freeBSD at least.

Duh, should've mentioned the version:

FreeBSD wattres.Watt.COM 6.2-PRERELEASE FreeBSD 6.2-PRERELEASE #6: Tue Dec 26 11:46:36 PST 2006     root at wattres.Watt.COM:/usr/obj/usr/src/sys/WATTRES  i386

I did the cvsup just before the build time above.

I just turned off net.inet.tcp.rfc1323; we'll see if that helps on the
next polling attempt by skype's server.

-- 
Steve Watt KD6GGD  PP-ASEL-IA          ICBM: 121W 56' 57.5" / 37N 20' 15.3"
 Internet: steve @ Watt.COM                      Whois: SW32-ARIN
   Free time?  There's no such thing.  It just comes in varying prices...