Subject: [rbridge] How are packets/link without a VLAN tag handled in a bridged network today?

From: harald at alvestrand.no (Harald Tveit Alvestrand)
Date: Wed, 04 Jan 2006 11:36:09 +0100

--On torsdag, desember 29, 2005 20:03:10 -0800 "Ghanwani, Anoop" 
<anoop.ghanwani at hp.com> wrote:

> As for (3), yes, a port can be a member of
> multiple VLANs.  In that case, untagged traffic
> arriving at the port gets assigned the PVID.
> When you send traffic out, there is a parameter
> to control whether or not a given VLAN should
> be tagged/untagged before sending the frame
> out.

Just to be sure I understand you correctly:

If an untagged frame arrives from the LAN to the switch, it gets assigned 
the PVID belonging to the port it arrives on (there can be only one).

The operator can configure the port to receive traffic for multiple VLANs, 
and can make the decision for each VLAN on the port whether to send out the 
frames on that port for that VLAN tagged or untagged.

Right?

(I can imagine some cases where it would be useful to send traffic from 
more than one VLAN untagged (if one VLAN is used to distribute 
unidirectional multicast traffic "broadcast-like" into all segments, for 
instance), but I agree that this could easily be confusing if the operator 
doesn't keeep things very straight in his head.... mixing tagged and 
untagged traffic would chiefly be useful (I think) if a link is used both 
to connect end-stations to bridges and to connect bridges, much as we 
imagine "internal" (in Joe's terms) traffic between RBridges flowing over 
the same physical LAN segments as "external" traffic.)

BTW... I couldn't find a place in 802.1Q that talks about *changing* VLAN 
IDs; is this a standard function or a "vendor extension"?

                      Harald