From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Greear Subject: Re: Linux, tcpdump and vlan Date: Thu, 19 Jul 2007 16:38:57 -0700 Message-ID: <469FF611.6080905@candelatech.com> References: <930446.33248.qm@web56601.mail.re3.yahoo.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Patrick McHardy , Stephen Hemminger , Krzysztof Halasa , linux-kernel@vger.kernel.org, Linux Netdev List To: andrei radulescu-banu Return-path: In-Reply-To: <930446.33248.qm@web56601.mail.re3.yahoo.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org andrei radulescu-banu wrote: > During debugging, I noticed that dev_queue_xmit() is called twice for tx vlan frames. This results in a frame being passed twice to a packet socket bound to 'any' interface. If the packet socket is bound to a specific interface, though, it will get only one copy of the tx frame, which is good. > > In more detail: suppose we're tx'ing a frame, and the route table lookup yields a vlan outgoing device eth0.2. dev_queue_xmit() is called, which calls dev_queue_xmit_nit() for dev = eth0.2 then dev->hard_start_xmit() for dev = eth0.2. > > The latter call gets into the vlan layer, which attaches the vlan id 2 (accelerated or not... in my e1000 case accelerated) then calls dev_queue_xmit() again. This time around dev_queue_xmit_nit() is called for dev = eth0, and dev->hard_start_xmit() actually calls the ethernet driver. > > The net result is that dev_queue_xmit_nit() is called twice, once for dev=eth0.2 then for dev=eth0. Maybe binding to all isn't such a good idea then. Ben -- Ben Greear Candela Technologies Inc http://www.candelatech.com