[rbridge] Consensus Check: C-Tags

[Eric Gray]

James,

	Not exactly.  It is my opinion that support for the use 
of S-TAGs _requires_ no further specification.  Consider the
following quote from 802.1Q-2006:

"The semantics and structure of the S-TAG is identical to that 
 of the C-TAG, with the exception that bit 5 in octet 1, the
 Drop Eligible Indicator (DEI) bit, does not convey a CFI (9.6).
 The priority and drop_eligible parameters are conveyed in the
 3-bit PCP field and the DEI bit as specified in 6.7.3."

	Given this description of the differences between C-TAGs
and S-TAGs, it seems quite reasonable to me to suppose that any
one wanting to support S-TAGs should be able to without further
specification in either the TRILL WG, or in the IETF.

	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.

	With this subtle distinction, we are probably otherwise
in agreement.

--
Eric Gray
Principal Engineer
Ericsson  

> -----Original Message-----
> From: James Carlson [mailto:james.d.carlson at sun.com] 
> Sent: Tuesday, April 08, 2008 10:24 AM
> 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:
> > 3) One way to get around this is to state - up-front - that the use 
> >    of C-TAGs is assumed in the protocol specification, but there is 
> >    no intention to prohibit use of S-TAGs, and probably further say
> >    that any additional specification required to support S-TAGs is
> >    out of scope in this protocol specification.
> 
> It sounds like we're in violent agreement: this specification uses
> C-tags, and S-tags are just out of scope.  A future document might
> address them.
> 
> -- 
> 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
>