Date: Wed, 2 Aug 2006 20:13:52 +1000 From: Peter Jeremy <peterjeremy@optushome.com.au> To: freebsd-net@freebsd.org Subject: TCP Retransmit counts Message-ID: <20060802101352.GD713@turion.vk2pj.dyndns.org>
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--u65IjBhB3TIa72Vp Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable I often need to move my laptop around the house and have temporary network outages (no wireless). I've noticed that any active TCP connections drop out fairly quickly - some checking with tcpdump shows that there is only 60 seconds between the first transmit attempt and the last re-transmit. This strikes me as excessively short - it's likely to take more time than this for a managed switch or router to reboot. I've previously (5-6 years ago) done some testing on other commercial Unices and got figures of 8-10 minutes - which seems more reasonable. Having had a look at the code, there are TCP_MAXRXTSHIFT (12) re-transmit attempts with exponential back-off based on the calculated RTT. Whilst this is probably reasonable for a WAN link, I would like to extend the timeout on LAN links. Can anyone see any downsides to either increasing TCP_MAXRXTSHIFT (and associated timer arrays) or changing retransmit timeout to having a minimum value (similar but opposite to the tcp_maxpersistidle test in tcp_timer_persist)? --=20 Peter Jeremy --u65IjBhB3TIa72Vp Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.4 (FreeBSD) iD8DBQFE0Hrg/opHv/APuIcRAh9GAJ9tQSEumj1xUE4G8UNe87YAV0eIpwCgms5/ ml7gnGSEEiiuDPKdcdQX26I= =LYyQ -----END PGP SIGNATURE----- --u65IjBhB3TIa72Vp--
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