From owner-freebsd-net@FreeBSD.ORG Fri Oct 17 12:20:50 2003 Return-Path: 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 7FF3716A4B3 for ; Fri, 17 Oct 2003 12:20:50 -0700 (PDT) Received: from mailtoaster1.pipeline.ch (mailtoaster1.pipeline.ch [62.48.0.70]) by mx1.FreeBSD.org (Postfix) with ESMTP id 00F8C43FF2 for ; Fri, 17 Oct 2003 12:20:49 -0700 (PDT) (envelope-from oppermann@pipeline.ch) Received: (qmail 89962 invoked from network); 17 Oct 2003 19:23:01 -0000 Received: from unknown (HELO pipeline.ch) ([62.48.0.53]) (envelope-sender ) by mailtoaster1.pipeline.ch (qmail-ldap-1.03) with SMTP for ; 17 Oct 2003 19:23:01 -0000 Message-ID: <3F9040AC.7F117AFA@pipeline.ch> Date: Fri, 17 Oct 2003 21:19:08 +0200 From: Andre Oppermann X-Mailer: Mozilla 4.76 [en] (Windows NT 5.0; U) X-Accept-Language: en MIME-Version: 1.0 To: Carl Mascott References: <200310171830.h9HIUnSr000572@callisto.local> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit cc: freebsd-net@freebsd.org Subject: Re: TCP window size issues X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 17 Oct 2003 19:20:50 -0000 Carl Mascott wrote: > > I have a few TCP window size issues. > > 1. In FreeBSD 4.8-R the kernel default recv window is 56 KB. This > is so large that it causes dropped packets due to queue overflow > with my V.90 link (BW 5 KB/s on compressed data). > > 2. The 4.4BSD TCP implementation has never had the correct precedence > rules for setting window sizes. App-set values should take > precedence over all others. Routing table values should take > precedence over kernel default values. The fix for PR 11966 > alters the behavior but still doesn't implement these precedence > rules. I'll fix this in my tcp_hostcache patch currently under review by Sam Leffler and Ruslan Ermilov (however that is for -CURRENT). > http://www.freebsd.org/cgi/query-pr.cgi?pr=11966 > > 3. RFC 793 (TCP) says that shrinking the receive window after > connection is established is "strongly discouraged". I'm > currently shrinking the receive window on my default route > (PPP link) from 32 KB to 4 KB with settings in > /etc/ppp/ppp.conf. (Had to back out patch in PR 11966.) > No problems noticed yet. To avoid shrinking the window I > believe I'd have to do the following: > > - set kernel default send & recv windows to smallest values > used on any route > > - modify all other routes on bootup (with script in > /usr/local/etc/rc.d ?) to set desired larger window sizes > > Keeping the script in sync with the routing table would be > a new maintenance headache. > > How likely am I to get into trouble by shrinking the TCP > receive window? Likely enough that I should make the > changes above? The patch in PR 11966 was kicking around > for about a year before the PR was filed. Was this patch > originally intended to solve a TCP compatibility problem > caused by shrinking the TCP receive window? -- Andre