[rbridge] Trivial (I hope) 802 VLAN encoding question

[Radia Perlman]

Is there a distinction between VLAN 0 and null VLAN? In other words, if 
there is
no VLAN tag, is that the same as being in VLAN 0?

I'm trying to specify how to distinguish the per-VLAN instance of IS-IS 
from the core instance.
I was assuming it would be done based on an inner VLAN tag. But suppose 
there were no VLANs,
but you still wanted different instances for the endnode information and 
the core information (so that
truly inner guys wouldn't have to store all the endnode membership link 
state information).
You couldn't do that with a VLAN tag, unless you used VLAN tag with 
VLAN=0 for the endnoe
membership instance.

Not a really horrible problem -- we can certainly find a way of encoding 
this, but just wondering if
VLAN tag will work (where we use VLAN tag explicitly with VLAN = 0 to 
indicate the endnode
membership inforamtion for the null VLAN?)

Radia