RE: dropping of un-matched tagged packets?

> Hello,
> 
> I've observed a behaviour of Linux VLAN support that surprises me,
but,
> given that I'm not an expert :) I would like to describe it in this
list,
> just to know if it is the expected behaviour.
> 
> It seems that when a 802.1q tagged packet is received in a physical
Linux
> interface (for example 'eth2') the behaviour is:
> 
> 1. If there is some subinterface maching the tag, the packet is
deliver to
> that interface. For example, if the packet is tagged with VLANID=200
and
> there is an eth2.200 interface, the packet is delivered to eth2.200
(and a
> 'tcpdump -i eth2.200', for example, would show it).
> 
> 2. If there is no subinterface maching the tag, the packet is drop.
For
> example, if the packet is tagged with VLANID=300 and there is no
eth2.300,
> the packet is drop (and a 'tcpdump -i eth2' would never show it).
> 
> Is that right?
> 
> In that case, I would like to know if is possible to change the
behaviour
> of
> item 2 (maybe with some configuration in the /proc/sys hierarchy), so
a
> 'tcpdump -i eth2' shows the tagged packet.
> 
> I'm asking this beacuse I would like to bridge a trunk of tagged
traffic
> (that comes at eth2 from/to a Cisco router) with a software bridge in
the
> Linux box implemeted with brctl ('brctl addif somebridge eth2') , but
if
> the
> default behaviour is to drop tagged un-matched packets, this seems
> imposible...

What Ethernet adapter are you using (chipset or linux module name)?

Do you have any ebtables rules in place (you will eventually need some
to do what you want to do)?

James