From owner-freebsd-questions@FreeBSD.ORG Thu Jun 19 09:37:14 2003 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 8678837B401 for ; Thu, 19 Jun 2003 09:37:14 -0700 (PDT) Received: from mailgw2a.lmco.com (mailgw2a.lmco.com [192.91.147.7]) by mx1.FreeBSD.org (Postfix) with ESMTP id A581943F3F for ; Thu, 19 Jun 2003 09:37:13 -0700 (PDT) (envelope-from koroush.saraf@lmco.com) Received: from emss01g01.ems.lmco.com ([129.197.181.54]) by mailgw2a.lmco.com (8.11.6p2/8.11.6) with ESMTP id h5JGbCv04135 for ; Thu, 19 Jun 2003 12:37:12 -0400 (EDT) Received: from CONVERSION-DAEMON.lmco.com by lmco.com (PMDF V6.1-1 #40643) id <0HGQ00N01LBBGR@lmco.com> for freebsd-questions@FreeBSD.ORG; Thu, 19 Jun 2003 09:37:08 -0700 (PDT) Received: from BSDWIN2KKOROUSH ([129.197.244.4]) by lmco.com (PMDF V6.1-1 #40643) with SMTP id <0HGQ00BM7LZ722@lmco.com> for freebsd-questions@FreeBSD.ORG; Thu, 19 Jun 2003 09:33:07 -0700 (PDT) Date: Thu, 19 Jun 2003 09:32:43 -0700 From: Koroush Saraf To: freebsd-questions@FreeBSD.ORG Message-id: <00a001c33680$68827600$04f4c581@BSDWIN2KKOROUSH> MIME-version: 1.0 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 X-Mailer: Microsoft Outlook Express 6.00.2800.1158 X-Priority: 3 X-MSMail-priority: Normal Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 7BIT X-Content-Filtered-By: Mailman/MimeDel 2.1.1 Subject: PMTUD Black Hole Problem X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 19 Jun 2003 16:37:14 -0000 Hi All, I have the following network in the lap WINXP <---mtu1500--->FREEBSD4.4<---mtu1280(gif tunnel--->FREEBSD4.4<---mtu1500--->WINXP The BSD computers are setup as gateway routers. As you might see from diagram above, the MTU of the link between the two BSD computers is 1280Bytes because of a tunnel. When I try to transfer a file between the XP endpoints, the PMTUD goes off by sending a 1514B packet to the other end with the Don't fragment bit set. However this packet never generates the ICMP unreachable message back to the XP box during Path MTU discovery. So that's why I have concluded that the BSD router is the black hole. Now I would like to know how to make my BSD router to participate in the MTU discovery. Changing the MTU of the windows computers is not an option for me. Also please note that the BSD computers only have one NIC interface, and the network is logically sperate but physically all connected to a switch, so playing with the MTU of the interface connecting the BSD computers is not an option either. I hope that this is a known problem and easy to fix and thanks for taking the time to respond. ~koroush