[rbridge] RBridge: a case of study

[Eastlake III Donald-LDE008]

See below at @@@

-----Original Message-----
From: James Carlson [mailto:james.d.carlson at sun.com] 
Sent: Wednesday, October 31, 2007 10:14 AM
To: Eric Gray
Cc: Eastlake III Donald-LDE008; Zhi-Hern Loh; Developing a hybrid
router/bridge.
Subject: Re: [rbridge] RBridge: a case of study

Eric Gray writes:
> Donald,
> 
> 	When you say "would all have the same Outer [VID]"
> - do you mean:
> 
> 1) all frames MUST have the same VID within the an RBridge 
>    campus, 
> 2) all frames forwarded from a (physical) port on one RBridge 
>    to a (physical) port on another RBridge MUST have the same
>    VID, or 
> 3) something else?

(I'm not Donald, but ...)

@@@ Well, I am Donald and I meant something like (2) but a bit narrower.
I would have said "all TRILL frames" because "all frames" is way too
inclusive. What about control frames like 802.1AB? Furthermore, in the
case of point-to-point links between two Rbridges (i.e., no bridges or
end station connections in between), as far as I can see there is no
particular utility in considering the TRILL frames to have any external
VLAN coloring and certainly no need for them to be outer tagged with a
VLAN ID or priority.

My understanding was more like:

  3) Where an outer VLAN tag is present, all frames transmitted by an
     RBridge must have the same inner and outer VLAN tag numbers.
     Where an outer VLAN tag is not present, the implicit tag for that
     port must match or be compatible with the inner tag.

... which would be consistent with "traditional" bridge behavior and
would effectively rule out the type of solution that Silvano Gai has
been proposing.

@@@ Well, your version of (3) above is, as I recall, roughly how things
were in draft -04. However, by -05 posted in July of this year (except
in the pseudo code which is clearly labeled as still being that from
-04), in order to actually provide the promised optimal pair-wise
routing, the Outer and Inner VLANs are completely decoupled. See, for
example, Section 4.1.2 of -05. And some recent proposals suggest using a
single Outer VLAN ID on a link. 

The distinction with (2) in your list is that (2) appears to rule out
the use of so-called "tagged" or leaf or ingress ports, forcing all
ports to carry VLAN tags.

@@@ I find your above statement a bit confusing. Item (2) seems to be
talking about TRILL frames between Rbridges which doesn't have anything
to do with ingressing native frames.

@@@ Thanks,
@@@ Donald

-- 
James Carlson, Solaris Networking              <james.d.carlson at sun.com>
Sun Microsystems / 35 Network Drive        71.232W   Vox +1 781 442 2084
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