From owner-freebsd-net@FreeBSD.ORG Tue Feb 13 16:51:55 2007 Return-Path: X-Original-To: freebsd-net@freebsd.org Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 742A616A406 for ; Tue, 13 Feb 2007 16:51:55 +0000 (UTC) (envelope-from Stephen.Clark@seclark.us) Received: from smtpout10-04.prod.mesa1.secureserver.net (smtpout10-04.prod.mesa1.secureserver.net [64.202.165.238]) by mx1.freebsd.org (Postfix) with SMTP id 44E5713C4B7 for ; Tue, 13 Feb 2007 16:51:55 +0000 (UTC) (envelope-from Stephen.Clark@seclark.us) Received: (qmail 7597 invoked from network); 13 Feb 2007 16:25:14 -0000 Received: from unknown (24.144.77.243) by smtpout10-04.prod.mesa1.secureserver.net (64.202.165.238) with ESMTP; 13 Feb 2007 16:25:14 -0000 Message-ID: <45D1E669.30402@seclark.us> Date: Tue, 13 Feb 2007 11:25:13 -0500 From: Stephen Clark User-Agent: Mozilla/5.0 (X11; U; Linux 2.2.16-22smp i686; en-US; m18) Gecko/20010110 Netscape6/6.5 X-Accept-Language: en-us, en MIME-Version: 1.0 To: freebsd-net@freebsd.org Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: pmtud problem X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: Stephen.Clark@seclark.us List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 13 Feb 2007 16:51:55 -0000 Hello List, We have a setup that looks like the following. pc <-ethernet-> freebsd 4.9 <-pppoe-> internet <-ethernet-> freebsd 6.1 on the freebsd box we have a gre tunnel with a mtu of 1420 feeding into a gif vpn tunnel with a mtu of 1280 ( I know this dumb but it the default value when you create a gif ) feeding into a tun0 with a mtu of 1492. What we see is the packet never makes it to the freebsd 6.1 system. if the pc sends a packet of 1460 bytes with the DF bit set shouldn't the freebsd 4.9 system send back an icmp dest unreachable - fragmentation needed and DF bit set? $ sysctl -a | grep mtu net.inet.tcp.path_mtu_discovery: 1 Now if I change the mtu of the gre to 1412 everything works. Any insight would be appreciated. Thanks, Steve -- "They that give up essential liberty to obtain temporary safety, deserve neither liberty nor safety." (Ben Franklin) "The course of history shows that as a government grows, liberty decreases." (Thomas Jefferson)