Subject: [rbridge] VLANs

From: Eric.Gray at marconi.com (Gray, Eric)
Date: Tue, 31 Oct 2006 12:03:34 -0500

Silvano,

	Actually, both "types" of VLANs are the same - applying at 
different layers, but defined using the same terminology.  Logic,
semantics and applicability are the same.

	For historic reasons, we are trying to avoid the terms you
propose.  In fact, similar terms have been used previously and 
removed as confusing.  Without constant reminders, "inner" and 
"outer" will be taken in some instances as placement in the frame 
(as you are suggesting) or position relative to the CRED (a usage
issue with the terms "ingress" and "egress" meaning "way in" and
"way out" respectively).

	Hence you are suggesting replacement with one potential 
are of confusion with another one we've earlier discarded.

	The architecture document defines the term VLAN and - I am
reasonably sure - uses that definition consistently.  Moreover,
the architecture document tries to be agnostic about the use of 
VLANs - particularly with respect to VLAN tagged encapsulation
and port-based VLANs, and where these things might apply.  The
reason for this is simply that one aim of protocol development - 
especially at the architectural level - should be to avoid placing
constraints on implementation beyond those explicitly required 
to ensure interoperability.

--
Eric

--> -----Original Message-----
--> From: rbridge-bounces at postel.org 
--> [mailto:rbridge-bounces at postel.org] On Behalf Of Silvano Gai
--> Sent: Monday, October 30, 2006 12:29 PM
--> To: rbridge at postel.org
--> Subject: [rbridge] VLANs
--> 
--> 
--> The second biggest issue I have with the four documents 
--> (first one being
--> broadcast/multicast storm) is the definition of VLANs.
--> 
--> I don't think the term VLAN is used consistently in the documents.
--> 
--> 1) Sometimes VLAN refers to the VLANs present on the 
--> untagged frames,
--> which must be propagated by ISIS, VLAN pruning must be 
--> performed and so
--> on. They all share the same core instance of ISIS.
--> 
--> 2) Sometimes VLANs refers to the fact that a CRED can be 
--> encapsulated
--> into a VLAN (present as a 1Q tag in the outer header) and 
--> therefore ISIS
--> will run per VLAN, i.e. there will be a core instance of 
--> ISIS per each
--> VLAN. This seems to be the case in some part of the architectural
--> document.
--> 
--> I propose to name the former IVLAN (inner VLAN) and the latter OVLAN
--> (Outer VLAN), with reference to the position of the 1Q tag 
--> in the frame.
--> 
--> This is also very relevant for the discussion that we need 
--> to complete
--> on the FTAG: it is my understanding that some folks think 
--> that the FTAG
--> is not needed, since there may be an OVLAN.
--> 
--> Comments?
--> 
--> -- Silvano
--> 
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