From owner-freebsd-net@FreeBSD.ORG Tue Feb 15 04:31:32 2005 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 A7C3E16A4CE for ; Tue, 15 Feb 2005 04:31:32 +0000 (GMT) Received: from wyvern.icir.org (wyvern.icir.org [192.150.187.14]) by mx1.FreeBSD.org (Postfix) with ESMTP id 8068B43D46 for ; Tue, 15 Feb 2005 04:31:32 +0000 (GMT) (envelope-from mallman@icir.org) Received: from guns.icir.org (adsl-68-76-113-50.dsl.bcvloh.ameritech.net [68.76.113.50]) by wyvern.icir.org (8.12.9p1/8.12.8) with ESMTP id j1F4VQTa089863; Mon, 14 Feb 2005 20:31:27 -0800 (PST) (envelope-from mallman@icir.org) Received: from lawyers.icir.org (guns.icir.org [68.76.113.50]) by guns.icir.org (Postfix) with ESMTP id 8FA3A77A349; Mon, 14 Feb 2005 23:31:24 -0500 (EST) Received: from lawyers.icir.org (localhost [127.0.0.1]) by lawyers.icir.org (Postfix) with ESMTP id A8907241AE3; Mon, 14 Feb 2005 23:31:25 -0500 (EST) To: Sam Jansen From: Mark Allman In-Reply-To: <420BCEF7.1080603@meta.net.nz> Organization: ICSI Center for Internet Research (ICIR) Song-of-the-Day: Thunderstruck MIME-Version: 1.0 Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha1; protocol="application/pgp-signature" Date: Mon, 14 Feb 2005 23:31:25 -0500 Sender: mallman@icir.org Message-Id: <20050215043125.A8907241AE3@lawyers.icir.org> cc: freebsd-net@freebsd.org Subject: Re: SACK problems X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list Reply-To: mallman@icir.org List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 15 Feb 2005 04:31:32 -0000 --=-=-= Content-Type: text/plain > During some testing on an isolated network we have, I found some > interesting behaviour from a FreeBSD 5.3 host using TCP SACK. > > I've detailed this problem fully at: > > http://www.wand.net.nz/~stj2/nsc/emu_freebsd.html > > PCAP traces and some screenshots from tcptrace graphs can be found > at the above link to show what is happening. It looks to me like > SACK blocks are being incorrectly generated in this example. I can't > think of any valid reason why a SACK block would SACK from below the > current ACK value to above it (which is the problem here). > > Thoughts, anyone? Am I just wrong here and this is valid, expected > behaviour? RFC2883 offers a case when this would happen --- in the reporting of "duplicate SACKs". I.e., the DSACK extension reports segments that have arrived more than once. I don't suppose this is the problem (since it's freebsd everywhere, right?). But, while folks are messing about in the SACK code this RFC might be something to think about including. allman -- Mark Allman -- ICIR -- http://www.icir.org/mallman/ --=-=-= Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.4 (Darwin) iD8DBQFCEXsdWyrrWs4yIs4RAj4iAJ9fkHmvFCw09AjbI1YN0UGv7xuYMQCfW3y3 gSuIcjNfO506s99weZriBv4= =Wjr3 -----END PGP SIGNATURE----- --=-=-=--