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RE: [Xen-devel] Problem with VLANs on tg3 NICs

To: "Nate Carlson" <natecars@xxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] Problem with VLANs on tg3 NICs
From: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>
Date: Fri, 19 Jan 2007 07:52:16 -0000
Cc: Evan Bigall <evan.bigall@xxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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Thread-topic: [Xen-devel] Problem with VLANs on tg3 NICs
> On Thu, 18 Jan 2007, Ian Pratt wrote:
> > I'm still a bit confused as to how the standard linux bridge can
work
> > with VLAN trunks. With a 'real' Ethernet switch you have to enable
which
> > VLANs you want to appear on a port. I'm not aware of the Linux
bridge
> > having such functionality -- I thought you had to set up a separate
> > bridge for each VLAN then mux/demux them at the physical/virtual
NICs.
> 
> You're thinking of VLAN-aware switches.. if you're using an unmanaged
> switch that doesn't have a concept of VLAN's (ie, the Linux bridging
code,
> IIRC), it'll just pass the packet on, tags and all.

If its broadcasting all VLAN-tagged traffic to all ports that's
disastrous for performance. You'd be much better off setting up a
separate bridge for each VLAN. Alternatively, it might be worth looking
at The Linux Switching Appliance (LISA) project -- their bridge supports
VLAN trunks.

Ian 

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