From mboxrd@z Thu Jan 1 00:00:00 1970 From: "pupilla@libero.it" Subject: per route MTU settings Date: Fri, 11 Jan 2013 17:29:28 +0100 (CET) Message-ID: <22271727.642511357921768466.JavaMail.defaultUser@defaultHost> Reply-To: "pupilla@libero.it" Mime-Version: 1.0 Content-Type: text/plain;charset="UTF-8" Content-Transfer-Encoding: 7bit To: netdev@vger.kernel.org Return-path: Received: from outrelay01.libero.it ([212.52.84.101]:47370 "EHLO outrelay01.libero.it" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754403Ab3AKQ33 (ORCPT ); Fri, 11 Jan 2013 11:29:29 -0500 Received: from wmail43 (172.31.0.232) by outrelay01.libero.it (8.5.140.03) id 50D43D7F026FA70F for netdev@vger.kernel.org; Fri, 11 Jan 2013 17:29:28 +0100 Sender: netdev-owner@vger.kernel.org List-ID: Hello everybody. I have done some tests with per route mtu settings. Here is the results on the 10.81.104.254 linux box running 3.6.9 on Slackware 14 32bit: ip route add 10.81.105.109/32 via 10.81.104.1 mtu lock 1450 ip route flush cache ping -M do 10.81.105.109 -c 5 -s 1450 PING 10.81.105.109 (10.81.105.109) 1450(1478) bytes of data. >>From 10.81.104.254 icmp_seq=1 Frag needed and DF set (mtu = 1450) >>From 10.81.104.254 icmp_seq=1 Frag needed and DF set (mtu = 1450) >>From 10.81.104.254 icmp_seq=1 Frag needed and DF set (mtu = 1450) >>From 10.81.104.254 icmp_seq=1 Frag needed and DF set (mtu = 1450) >>From 10.81.104.254 icmp_seq=1 Frag needed and DF set (mtu = 1450) Here is the results on my linux box with ip address 10.81.104.126 (the default gateway is 10.81.104.254) running linux 3.7.0 on Slackware 14 64bit ping -M do 10.81.105.109 -c 5 -s 560 PING 10.81.105.109 (10.81.105.109) 560(588) bytes of data. >>From 10.81.104.254 icmp_seq=1 Frag needed and DF set (mtu = 576) >>From 10.81.104.126 icmp_seq=2 Frag needed and DF set (mtu = 576) >>From 10.81.104.126 icmp_seq=2 Frag needed and DF set (mtu = 576) >>From 10.81.104.126 icmp_seq=2 Frag needed and DF set (mtu = 576) >>From 10.81.104.126 icmp_seq=2 Frag needed and DF set (mtu = 576) When packets are generated locally (on the 10.81.104.254 box), linux icmp message 'need to frag' report the correct mtu of next hop. Instead on the forwarded packets (those that aren't originated on the 10.81.104.254 box), I always get the 576 value on the mtu of nexthop. Is this the expected behaviour? Any response are welcome TIA