From owner-svn-src-all@FreeBSD.ORG Wed Sep 15 16:14:48 2010 Return-Path: Delivered-To: svn-src-all@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id BFB481065741; Wed, 15 Sep 2010 16:14:48 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from cyrus.watson.org (cyrus.watson.org [65.122.17.42]) by mx1.freebsd.org (Postfix) with ESMTP id 8D36A8FC15; Wed, 15 Sep 2010 16:14:48 +0000 (UTC) Received: from bigwig.baldwin.cx (66.111.2.69.static.nyinternet.net [66.111.2.69]) by cyrus.watson.org (Postfix) with ESMTPSA id 3016446C18; Wed, 15 Sep 2010 12:14:48 -0400 (EDT) Received: from jhbbsd.localnet (smtp.hudson-trading.com [209.249.190.9]) by bigwig.baldwin.cx (Postfix) with ESMTPSA id 00ABA8A051; Wed, 15 Sep 2010 12:14:46 -0400 (EDT) From: John Baldwin To: Andre Oppermann Date: Wed, 15 Sep 2010 12:12:52 -0400 User-Agent: KMail/1.13.5 (FreeBSD/7.3-CBSD-20100819; KDE/4.4.5; amd64; ; ) References: <201009151039.o8FAdU4H030416@svn.freebsd.org> <4C90B326.4000208@freebsd.org> <4C90D27D.4070306@freebsd.org> In-Reply-To: <4C90D27D.4070306@freebsd.org> MIME-Version: 1.0 Content-Type: Text/Plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <201009151212.52337.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.0.1 (bigwig.baldwin.cx); Wed, 15 Sep 2010 12:14:47 -0400 (EDT) X-Virus-Scanned: clamav-milter 0.95.1 at bigwig.baldwin.cx X-Virus-Status: Clean X-Spam-Status: No, score=-2.6 required=4.2 tests=AWL,BAYES_00 autolearn=ham version=3.2.5 X-Spam-Checker-Version: SpamAssassin 3.2.5 (2008-06-10) on bigwig.baldwin.cx Cc: svn-src-head@freebsd.org, Lawrence Stewart , svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r212653 - head/sys/netinet X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 15 Sep 2010 16:14:48 -0000 On Wednesday, September 15, 2010 10:04:45 am Andre Oppermann wrote: > Below is the wording proposed by Lawrence: > /* > * The default Maximum Segment Size (MSS) to use when we do not have specific > * knowledge (e.g. via path MTU discovery) that the destination host is prepared > * to accept larger datagrams. The smallest allowable IP datagram MTU and > * optionless IP/TCP header lengths are used for the calculation as per RFC879. > * For IPv4 (RFC791): 576 - 20 - 20 = 536. > * For IPv6 (RFC2460): 1280 - 40 - 20 = 1220. > */ > #define TCP_MSS 536 > #define TCP6_MSS 1220 I think the existing text is fine for this comment, with one nit: * For IPv4 the MSS is 576 - sizeof(struct tcpiphdr) I would find it clearer if it was 'sizeof(struct ip) - sizeof(struct tcphdr)' instead. > * Limit the lowest MSS we accept for path MTU discovery and the TCP SYN MSS > * option. Allowing low values of MSS can consume significant resources and be > * used to mount a resource exhaustion attack. Connections requesting lower MSS > * values will be rounded up to this value and the IP_DF flag will be cleared to > * allow fragmentation along the path. > * > * See tcp_subr.c tcp_minmss SYSCTL declaration for more comments. Setting this > * SYSCTL to "0" disables the minmss check. > * > * The default value is fine for TCP over IPv4 across the Internet's smallest > * known link MTU (256 bytes for AX.25 packet radio). However, a connection is > * very unlikely to come across such low MTU interfaces (anno domini 2003). > */ > #define TCP_MINMSS 216 I actually prefer the above text for this block. The 'amounts of resources' phrase is certainly redundant and just 'resources' is clearer. -- John Baldwin