[rbridge] Consensus Check: C-Tags
james.d.carlson at sun.com
Tue Apr 8 11:03:23 PDT 2008
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>
Sun Microsystems / 35 Network Drive 71.232W Vox +1 781 442 2084
MS UBUR02-212 / Burlington MA 01803-2757 42.496N Fax +1 781 442 1677
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