Date: Mon, 01 Jan 2007 23:56:58 -0800 From: Julian Elischer <julian@elischer.org> To: Steve Watt <steve@Watt.COM> Cc: hackers@freebsd.org Subject: Re: Interesting TCP issue Message-ID: <459A104A.2000106@elischer.org> In-Reply-To: <200701012136.l01Lawp7017696@wattres.watt.com> References: <200701012136.l01Lawp7017696@wattres.watt.com>
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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> > 0x0000: 4520 004a 3260 4000 3a06 c609 d5f4 aa50 E..J2`@.:......P > 0x0010: 425d 8582 c4e6 0019 f2bc e212 4a6b fcff B]..........Jk.. > 0x0020: 8018 002e 9297 0000 0101 080a 95b8 5568 ..............Uh > 0x0030: 1eff 784a 4548 4c4f 2073 6861 7265 2e73 ..xJEHLO.share.s > 0x0040: 6b79 7065 2e6e 6574 0d0a kype.net.. > 0x0000: 4520 004a 3261 4000 3a06 c608 d5f4 aa50 E..J2a@.:......P > 0x0010: 425d 8582 c4e6 0019 f2bc e212 4a6b fcff B]..........Jk.. > 0x0020: 8018 002e 1d67 0000 0101 080a 95b8 ca98 .....g.......... > 0x0030: 1eff 784a 4548 4c4f 2073 6861 7265 2e73 ..xJEHLO.share.s > 0x0040: 6b79 7065 2e6e 6574 0d0a kype.net.. > > 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.
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