From owner-freebsd-net@FreeBSD.ORG Mon Apr 16 22:18:41 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 9CDD916A402; Mon, 16 Apr 2007 22:18:41 +0000 (UTC) (envelope-from jmg@hydrogen.funkthat.com) Received: from hydrogen.funkthat.com (gate.funkthat.com [69.17.45.168]) by mx1.freebsd.org (Postfix) with ESMTP id 1635613C465; Mon, 16 Apr 2007 22:18:41 +0000 (UTC) (envelope-from jmg@hydrogen.funkthat.com) Received: from hydrogen.funkthat.com (ox2qot40sjjyr9fy@localhost.funkthat.com [127.0.0.1]) by hydrogen.funkthat.com (8.13.6/8.13.3) with ESMTP id l3GLfp3I019928; Mon, 16 Apr 2007 14:41:51 -0700 (PDT) (envelope-from jmg@hydrogen.funkthat.com) Received: (from jmg@localhost) by hydrogen.funkthat.com (8.13.6/8.13.3/Submit) id l3GLfnmO019927; Mon, 16 Apr 2007 14:41:49 -0700 (PDT) (envelope-from jmg) Date: Mon, 16 Apr 2007 14:41:48 -0700 From: John-Mark Gurney To: Tom Judge Message-ID: <20070416214148.GX73385@funkthat.com> Mail-Followup-To: Tom Judge , freebsd-net@freebsd.org, FreeBSD Stable List References: <4623B0A2.5020006@tomjudge.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4623B0A2.5020006@tomjudge.com> User-Agent: Mutt/1.4.2.1i X-Operating-System: FreeBSD 5.4-RELEASE-p6 i386 X-Files: The truth is out there X-URL: http://resnet.uoregon.edu/~gurney_j/ X-Resume: http://resnet.uoregon.edu/~gurney_j/resume.html Cc: freebsd-net@freebsd.org, FreeBSD Stable List Subject: Re: Possible mtu bug in vlan or bce X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: John-Mark Gurney List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 16 Apr 2007 22:18:41 -0000 Tom Judge wrote this message on Mon, Apr 16, 2007 at 18:21 +0100: > I have seen some strange behaviour today with VLAN interfaces on bce > interfaces. I am running 6.2 Release on i386. > > I have a bce interface setup on a gig-e network with an MTU of 8192 i > attach a vlan interface to this and chnage the vlan if mtu to 1500 as it > has 100Mbit devices on it. This does not seem to affect the MTU of the > bce interface, the VLAN mtu is reported as changed by if config but the > bce is not reported as changed. However I then start to get error > messages saying that the NFS server is not responding as it is sending > packets larger than 1500 bytes. > > > If I try to raise the mtu of the vlan interface (to 8192 which is the > value that ifconfig reports for bce0) at this stage ifconfig thows an > error saying that the value is incorrect. If I then 'raise' (it already > appears to be set to 8192 according to ifconfig) the mtu of bce0 to 8192 > and then set the vlan interface mtu to 8192 the nfs server starts to > work again. Make sure that you change the host route's mtu down to the new MTU... I changed the MTU behavior a while back so that you could have a mixed network and support both large and regular sized MTU's on the same nextwork... # ifconfig em0 em0: flags=8843 mtu 9000 options=18b inet6 fe80::207:e9ff:fe0d:ad06%em0 prefixlen 64 scopeid 0x2 inet 192.168.0.21 netmask 0xffffff00 broadcast 192.168.0.255 ether 00:07:e9:0d:ad:06 media: Ethernet autoselect (1000baseTX ) status: active # netstat -rnWfinet Routing tables Internet: Destination Gateway Flags Refs Use Mtu Netif Expire default 192.168.0.14 UGS 0 8024 1500 em0 [...] 192.168.0.18 00:c0:f0:42:23:87 UHLW 1 2 1500 em0 1193 # route change 192.168.0.18 -mtu 9000 change host 192.168.0.18 # netstat -rnWfinet Routing tables Internet: Destination Gateway Flags Refs Use Mtu Netif Expire [...] 192.168.0.18 00:c0:f0:42:23:87 UHLW 1 2 9000 em0 1172 # ifconfig em0 mtu 1500 # ifconfig em0 em0: flags=8843 mtu 1500 options=18b inet6 fe80::207:e9ff:fe0d:ad06%em0 prefixlen 64 scopeid 0x2 inet 192.168.0.21 netmask 0xffffff00 broadcast 192.168.0.255 ether 00:07:e9:0d:ad:06 media: Ethernet autoselect (1000baseTX ) status: active # netstat -rnWfinet Routing tables Internet: Destination Gateway Flags Refs Use Mtu Netif Expire [..] 192.168.0.18 00:c0:f0:42:23:87 UHLW 1 2 9000 em0 1128 Hmmm... We may want to add code that detects when the host route's MTU is larger than the interface, and prevent that from happening. Though if an mtu daemon ever gets written, then that should take care of it. -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."