[rbridge] Consensus Check: C-Tags

[James Carlson]

Eric Gray writes:
> 	Hence the subtle issue is that - while I can agree with a
> statement that use of S-TAGs is out of scope in this version of
> the protocol specification - I agree with what I believe Dinesh
> was saying when he indicated that we should not prohibit use of
> S-TAGs in this specification by including a statement to the 
> effect that S-TAGs are not used.  Any statement such as "S-TAGs
> are not used" is innappropriate.  Further, I suggested using a
> phrase to the effect that while the specification assumes use
> of C-TAGS, it does not explicitly prohibit the use of S-TAGs.
> While S-TAG use may be out of scope for this specification, it
> may or may not require further specification (which means it is 
> also out-of-scope to make any assertion about whether, or not,
> additional specification is needed).

At the level that you're describing S-tags, any equipment that
understands an ordinary C-tag would perform the right functions,
leaving the issue essentially moot.

I read Donald's comments differently.  Equipment that processes what
are *known* to be S-tags should be dealing with the 'I' bits as well
and should know about provider-based bridging.  The current RBridges
specification does not do that.

So, sure, if you have packets on the wire that happens to look like
they have C-tags, and you don't tell an RBridge otherwise, then it'll
just do the right thing with respect to interpreting it as a VLAN.  It
won't look for the nested headers, though.

For that reason, I think our current spec leaves S-tags out of scope.
You're on your own if you use them with RBridges.  If someone cares
enough about S-tags to do them right, a future document _should_
discuss how to do that.  It shouldn't be the base document, though,
and we shouldn't discuss how to use them in that text.

-- 
James Carlson, Solaris Networking              <james.d.carlson at sun.com>
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