Date: Fri, 8 Feb 2013 02:50:21 -0800 From: Doug Hardie <bc979@lafn.org> To: freebsd-questions@FreeBSD.org Subject: Unusual TCP/IP Packet Size Message-ID: <28DC0F1E-EF32-4C77-9E09-27CC103265A4@lafn.org>
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Monitoring a tcpdump between two systems, a FreeBSD 9.1 system has the = following interface: msk0: flags=3D8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu = 1500 = options=3Dc011b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,TSO4,VLAN_HWTSO,LINK= STATE> ether 00:11:2f:2a:c7:03 inet 10.0.1.199 netmask 0xffffff00 broadcast 10.0.1.255 inet6 fe80::211:2fff:fe2a:c703%msk0 prefixlen 64 scopeid 0x1=20 nd6 options=3D29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL> media: Ethernet autoselect (100baseTX = <full-duplex,flowcontrol,rxpause,txpause>) status: active It sent the following packet: (data content abbreviated) 02:14:42.081617 IP 10.0.1.199.443 > 10.0.1.2.61258: Flags [P.], seq = 930:4876, ack 846, win 1040, options [nop,nop,TS val 401838072 ecr = 920110183], length 3946 0x0000: 4500 0f9e ea89 4000 4006 2a08 0a00 01c7 = E.....@.@.*..... 0x0010: 0a00 0102 01bb ef4a ece1 680b ae37 1bbc = .......J..h..7.. 0x0020: 8018 0410 3407 0000 0101 080a 17f3 8ff8 ....4...=85=85. The indicated packet length is 3946 and the load of data shown is that = size. The MTU on both interfaces is 1500. The receiving system = received 3 packets. There is a router and switch between them. One of = them fragmented that packet. This is part of a SSL/TLS exchange and one = side or the other is hanging on this and just dropping the connection. = I suspect the packet size is the issue. ssldump complains about the = packet too and stops monitoring. Could this possibly be related to the = hardware checksums?
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