[rbridge] Optional pseudonode

[James Carlson]

Radia Perlman writes:
> The notion of automatic pseudonode minimization was apparently discussed 
> at the last IETF in either rtgwg or IS-IS. I wasn't
> there, but heard there was not much interest, because there is already a 
> solution to that (configuration).

Not just that there was a solution, but what I heard was that it
"didn't matter."  In other words, if you configure everything as
multiple-access and needing a pseudo-node, who cares?  You get a small
increase in the number of LSPs, modern CPUs are fast, added complexity
(of any kind) is a bad thing, and so on.

> The reason it was brought up outside of TRILL was because some people 
> thought it was a good enough idea to
> deploy in IS-IS in general, an perhaps even OSPF.
> 
> In a lot of TRILL deployments all the links will be pt-to-pt (bridges 
> and shared media would have gone away), so it does

Exactly; that's why it's so much more interesting for us than for the
general case, and probably why it won't necessarily get traction
elsewhere.

> When the DRB decides to use a zero for pseudonode does not need to be 
> standardized, though we could give hints.
> It could be configured ("if you are DRB, always use a pseudonode", or 
> "never use a pseudonode").
> Or it could use an algorithm such as "if  you have only 1 RBridge 
> adjacency, don't use a pseudonode, but otherwise
> use a pseudonode". or "if you have 2 or more RBridge adjacencies, or had 
> 2 or more adjacencies within the last hour, use
> a pseudonode, otherwise don't".

I'd be in favor of the second suggested implementation -- it's simple
enough -- but obviously if one node makes the decision, it's no longer
a compatibility issue.

-- 
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