Messages in this thread | | | Date | Thu, 19 Jul 2007 16:38:57 -0700 | From | Ben Greear <> | Subject | Re: Linux, tcpdump and vlan |
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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 <greearb@candelatech.com> Candela Technologies Inc http://www.candelatech.com
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