From mboxrd@z Thu Jan 1 00:00:00 1970 From: "pupilla@libero.it" Subject: R: RE: per route MTU settings Date: Mon, 14 Jan 2013 09:51:53 +0100 (CET) Message-ID: <30645799.1106291358153513079.JavaMail.defaultUser@defaultHost> Reply-To: "pupilla@libero.it" Mime-Version: 1.0 Content-Type: text/plain;charset="UTF-8" Content-Transfer-Encoding: 7bit To: , Return-path: Received: from outrelay02.libero.it ([212.52.84.102]:35652 "EHLO outrelay02.libero.it" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755495Ab3ANIvz (ORCPT ); Mon, 14 Jan 2013 03:51:55 -0500 Sender: netdev-owner@vger.kernel.org List-ID: luky-37@hotmail.com wrote: >I guess 10.81.104.1 has a 576B MTU route/interface towards >10.81.105.109, no, 10.81.104.1 is only a L3 switch. >Running from both hosts pings with: >-s 548 >-s 549 >-s 1422 >-s 1423 > >and then analyzing the results will probably give us a better >idea of what actually happens. here is the results: root@10.81.104.254:~# ip route add 10.81.105.121/32 via 10.81.104.1 mtu lock 1450 root@10.81.104.254:~# ip r s | grep 10.81 | grep eth2 10.81.104.0/24 dev eth2 proto kernel scope link src 10.81.104.254 10.81.104.0/21 via 10.81.104.1 dev eth2 10.81.105.121 via 10.81.104.1 dev eth2 mtu lock 1450 root@10.81.104.254:~# ip route flush cache root@10.81.104.254:~# ping -M do 10.81.105.121 -c 4 -s 548 PING 10.81.105.121 (10.81.105.121) 548(576) bytes of data. 556 bytes from 10.81.105.121: icmp_req=1 ttl=127 time=0.476 ms 556 bytes from 10.81.105.121: icmp_req=2 ttl=127 time=0.448 ms 556 bytes from 10.81.105.121: icmp_req=3 ttl=127 time=0.515 ms root@10.81.104.254:~# ip route flush cache root@10.81.104.254:~# ping -M do 10.81.105.121 -c 4 -s 549 PING 10.81.105.121 (10.81.105.121) 549(577) bytes of data. 557 bytes from 10.81.105.121: icmp_req=1 ttl=127 time=0.386 ms 557 bytes from 10.81.105.121: icmp_req=2 ttl=127 time=0.525 ms 557 bytes from 10.81.105.121: icmp_req=3 ttl=127 time=0.447 ms root@10.81.104.254:~# ip route flush cache root@10.81.104.254:~# ping -M do 10.81.105.121 -c 4 -s 1422 PING 10.81.105.121 (10.81.105.121) 1422(1450) bytes of data. 1430 bytes from 10.81.105.121: icmp_req=1 ttl=127 time=0.724 ms 1430 bytes from 10.81.105.121: icmp_req=2 ttl=127 time=0.785 ms 1430 bytes from 10.81.105.121: icmp_req=3 ttl=127 time=1.95 ms root@10.81.104.254:~# ip route flush cache root@10.81.104.254:~# ping -M do 10.81.105.121 -c 4 -s 1423 PING 10.81.105.121 (10.81.105.121) 1423(1451) 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) root@10.81.104.126:~# ip r s default via 10.81.104.254 dev eth0 metric 1 10.81.104.0/24 dev eth0 proto kernel scope link src 10.81.104.126 127.0.0.0/8 dev lo scope link root@10.81.104.126:~# ping -M do 10.81.105.121 -c 4 -s 548 PING 10.81.105.121 (10.81.105.121) 548(576) bytes of data. 556 bytes from 10.81.105.121: icmp_req=1 ttl=127 time=0.352 ms 556 bytes from 10.81.105.121: icmp_req=2 ttl=127 time=0.372 ms 556 bytes from 10.81.105.121: icmp_req=3 ttl=127 time=0.368 ms root@10.81.104.126:~# ip route flush cache root@10.81.104.126:~# ping -M do 10.81.105.121 -c 4 -s 549 PING 10.81.105.121 (10.81.105.121) 549(577) bytes of data. >>From 10.81.104.254 icmp_seq=1 Frag needed and DF set (mtu = 576) I don't undestand why 10.81.104.254 here, is reporting that the mtu is 576 instead of 1450 >>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) root@10.81.104.126:~# ip route flush cache root@10.81.104.126:~# ping -M do 10.81.105.121 -c 4 -s 1422 PING 10.81.105.121 (10.81.105.121) 1422(1450) 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) root@10.81.104.126:~# ip route flush cache root@10.81.104.126:~# ping -M do 10.81.105.121 -c 4 -s 1423 PING 10.81.105.121 (10.81.105.121) 1423(1451) 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)