[rbridge] Consensus Check: C-Tags

[Eric Gray]

James,

	Perhaps the subtlety was lost on you, or perhaps I am
reading something into the proposed consensus suggested by
Donald.  Part of what Donald proposed as a consensus was:

"[The protocol specification] should not mention or use S-tags, 
except possibly to distinguish them from C-tags, state that 
they are not used, or the like."

I believe it was the statement "they are not used" that formed
the basis of Dinesh' comments:

"Why did we decide this ?"

- and -

"I'm fine with stating only about C-tags and not mention anything 
 about S-tags. I wouldn't want the spec to explicitly prohibit the 
 use of S-tags."

Donald responded to this with:

"I'm not sure exactly what you mean by 'explicitly prohibit the
 use of S-tags' but wherever the protocol spec requires a VLAN 
 tag (Outer or Inner), it currently specifies the use of the
 C-tag Ethertype.

"It is my impression that people are thinking that the current
 protocol spec is for customer Rbridges and that, perhaps, at
 some point in the future a separate 'provider Rbridge' document
 could be written which talks about S-tags, etc."

	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).

--
Eric Gray
Principal Engineer
Ericsson  

> -----Original Message-----
> From: James Carlson [mailto:james.d.carlson at sun.com] 
> Sent: Tuesday, April 08, 2008 1:10 PM
> To: Eric Gray
> Cc: Eastlake III Donald-LDE008; Dinesh G Dutt; Caitlin 
> Bestler; Rbridge at postel.org
> Subject: RE: [rbridge] Consensus Check: C-Tags
> Importance: High
> 
> Eric Gray writes:
> > 	However, it is possible that additional specification may
> > be needed.  Any such additional specification could be treated 
> > as out of scope (for now).  To tell the truth, I am unconvinced
> > of the need to do that - but I can live with a WG decision to
> > do so.
> > 
> > 	But it is essentially wrong - IMHO - to assert that S-TAG
> > use cannot be done without further specification.
> 
> Out of scope == not addressed by this specification.
> 
> Once we've called it "out of scope," I don't really care whether an
> additional document is _needed_ to complete that effort.  I suspect
> one will be needed, and you seem to be asserting that one will not,
> but I also think that it's completely immaterial for this document.
> 
> Ruling it out of scope means that we don't have to have the discussion
> about what (if anything) to do about provider bridging _now_.
> 
> -- 
> James Carlson, Solaris Networking              
> <james.d.carlson at sun.com>
> Sun Microsystems / 35 Network Drive        71.232W   Vox +1 
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> 781 442 1677
>