From owner-freebsd-net@freebsd.org Mon Jul 13 08:33:50 2015 Return-Path: Delivered-To: freebsd-net@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id DEDF799BC12 for ; Mon, 13 Jul 2015 08:33:50 +0000 (UTC) (envelope-from kpielorz_lst@tdx.co.uk) Received: from mail.tdx.com (mail.tdx.com [62.13.128.18]) by mx1.freebsd.org (Postfix) with ESMTP id AE8FB19B3 for ; Mon, 13 Jul 2015 08:33:49 +0000 (UTC) (envelope-from kpielorz_lst@tdx.co.uk) Received: from [10.12.30.106] (vpn01-01.tdx.co.uk [62.13.130.213]) (authenticated bits=0) by mail.tdx.com (8.14.3/8.14.3/) with ESMTP id t6D8XfDG014163 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 13 Jul 2015 09:33:42 +0100 (BST) Date: Mon, 13 Jul 2015 09:33:42 +0100 From: Karl Pielorz To: John-Mark Gurney cc: freebsd-net@freebsd.org Subject: Re: lagg of em0/em1 + VLAN = lower MTU? Message-ID: In-Reply-To: <20150710180627.GA8523@funkthat.com> References: <7CFE75F7566F5789DAD9FBB2@[10.12.30.106]> <20150710180627.GA8523@funkthat.com> X-Mailer: Mulberry/4.0.8 (Win32) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 13 Jul 2015 08:33:51 -0000 --On 10 July 2015 11:06 -0700 John-Mark Gurney wrote: > Try bumping the MTU on the root em's by 4 (1504) before creating the > lagg... I had thought of that - but didn't want to try it (on the basis that out of all the other example config's I've seen - no one else has to, and it will break the lagg MTU). Anyway I tried it, by: - Bump the MTU on the em interfaces before creating the lagg to 1504 - The lagg created, inherits this 1504 MTU That breaks the untagged IP on lagg0 - i.e. I end up with: " lagg0: flags=8843 metric 0 mtu 1504 options=4019b ether 68:05:ca:08:1d:3b inet x.x.x.x netmask 0xffffff00 broadcast y.y.y.y " That MTU of 1504 is going to break lagg0 for untagged traffic :( - However, the VLAN's setup on the lagg still default to 1496 MTU (despite the underlying interface lagg0 being MTU 1504) If I 'manually' bump the MTU on the individual lagg0.x VLAN interfaces - they will go to 1500, but traffic is still 'broken'. I can't 'reduce' the bad MTU on lagg0 either - i.e. 'ifconfig lagg0 mtu 1500' (to try to put it back to 1500) fails with an ioctl error. So sadly, I'm still stuck :( Something is lopping 4 bytes off the MTU when it shouldn't need to. None of the example configs I could find were from 10.1-R (or with exactly the same cards) - but obviously this is just bread & butter lagg/VLAN stuff, so it should work? -Karl