From owner-freebsd-net@FreeBSD.ORG Wed Aug 2 10:13:56 2006 Return-Path: X-Original-To: freebsd-net@freebsd.org Delivered-To: freebsd-net@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 4AE4216A4DA for ; Wed, 2 Aug 2006 10:13:56 +0000 (UTC) (envelope-from peterjeremy@optushome.com.au) Received: from mail17.syd.optusnet.com.au (mail17.syd.optusnet.com.au [211.29.132.198]) by mx1.FreeBSD.org (Postfix) with ESMTP id 8D4FB43D46 for ; Wed, 2 Aug 2006 10:13:55 +0000 (GMT) (envelope-from peterjeremy@optushome.com.au) Received: from turion.vk2pj.dyndns.org (c220-239-19-236.belrs4.nsw.optusnet.com.au [220.239.19.236]) by mail17.syd.optusnet.com.au (8.12.11/8.12.11) with ESMTP id k72ADr3D027012 (version=TLSv1/SSLv3 cipher=EDH-RSA-DES-CBC3-SHA bits=168 verify=NO) for ; Wed, 2 Aug 2006 20:13:54 +1000 Received: from turion.vk2pj.dyndns.org (localhost.vk2pj.dyndns.org [127.0.0.1]) by turion.vk2pj.dyndns.org (8.13.6/8.13.6) with ESMTP id k72ADqkw001513 for ; Wed, 2 Aug 2006 20:13:52 +1000 (EST) (envelope-from peter@turion.vk2pj.dyndns.org) Received: (from peter@localhost) by turion.vk2pj.dyndns.org (8.13.6/8.13.6/Submit) id k72ADqfT001512 for freebsd-net@freebsd.org; Wed, 2 Aug 2006 20:13:52 +1000 (EST) (envelope-from peter) Date: Wed, 2 Aug 2006 20:13:52 +1000 From: Peter Jeremy To: freebsd-net@freebsd.org Message-ID: <20060802101352.GD713@turion.vk2pj.dyndns.org> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="u65IjBhB3TIa72Vp" Content-Disposition: inline X-PGP-Key: http://members.optusnet.com.au/peterjeremy/pubkey.asc User-Agent: Mutt/1.5.11 Subject: TCP Retransmit counts X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 02 Aug 2006 10:13:56 -0000 --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--