From owner-freebsd-net@FreeBSD.ORG Fri Aug 12 19:52:26 2005 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 A871116A43D for ; Fri, 12 Aug 2005 19:52:26 +0000 (GMT) (envelope-from cswiger@mac.com) Received: from pi.codefab.com (pi.codefab.com [199.103.21.227]) by mx1.FreeBSD.org (Postfix) with ESMTP id 4DE1343D45 for ; Fri, 12 Aug 2005 19:52:26 +0000 (GMT) (envelope-from cswiger@mac.com) Received: from localhost (localhost [127.0.0.1]) by pi.codefab.com (Postfix) with ESMTP id BFA3A5F26; Fri, 12 Aug 2005 15:52:25 -0400 (EDT) Received: from pi.codefab.com ([127.0.0.1]) by localhost (pi.codefab.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 39071-07; Fri, 12 Aug 2005 15:52:24 -0400 (EDT) Received: from [192.168.1.3] (pool-68-161-79-217.ny325.east.verizon.net [68.161.79.217]) by pi.codefab.com (Postfix) with ESMTP id 445B95CBE; Fri, 12 Aug 2005 15:52:24 -0400 (EDT) Message-ID: <42FCFDFC.2020903@mac.com> Date: Fri, 12 Aug 2005 15:52:28 -0400 From: Chuck Swiger Organization: The Courts of Chaos User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.11) Gecko/20050801 X-Accept-Language: en-us, en MIME-Version: 1.0 To: jha miku References: <20050812020814.30073.qmail@web34105.mail.mud.yahoo.com> In-Reply-To: <20050812020814.30073.qmail@web34105.mail.mud.yahoo.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Virus-Scanned: amavisd-new at codefab.com Cc: freebsd-net@freebsd.org Subject: Re: Question regd timestamp option 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: Fri, 12 Aug 2005 19:52:26 -0000 jha miku wrote: > In case of active open, the SYN segments always have > timestamp enabled, since the RFC flg is set. But, > Currently, I am seeing some SYN segments without > timestamp option. FreeBSD (and OS X, and other things using a BSD network stack) will generate initial TCP SYN packets containing the "MNWNNT" TCP options, at least by default in the absense of other information or settings. > The only condition that I am aware of when timestamp > is disabled, is on sending the 3rd SYN in retransmit code > when the timestamp gets disabled. > looking at the tcpdump, it is unclear why the SYNs are > sent during active open without timestamp option. The TCP stack seems to remember some information about which TCP options a remote host is willing to accept. If the remote system didn't accept a timestamp the first time (perhaps it's talking to an old windows box which does "MNNS"), there is no point in sending that option out the next time you open a new connection to the same system. -- -Chuck