[rbridge] two minor issues with the isis-02 draft

[James Carlson]

The good news is that I'm done with this pass over our source code and
the relevant TRILL documents, so you likely won't hear many more
issues out of me for a while.  There's light at the end of the
tunneling protocol.


First issue: why does isis-02 specify the following?

   1. Information on reachable RBridge neighbors and the cost of the hop
      via the Extended IS Reachability TLV (Type #22) [RFC5305] (wide
      metric). TRILL IS-IS does not use the IS Reachability TLV (Type
      #2) (narrow metric).

This restriction doesn't appear to be necessary, and for bridges that
don't need the extended metrics, it seems slightly wasteful.  If
there's a purpose behind this (I have a bug filed against our code, as
we're still using #2), it'd be helpful to spell that purpose out
here.

(I was unable to find anything in protocol-11 that supported the need
for this particular restriction, though it's possible I missed
something.)


Second issue: the following mechanism from protocol-11 seems to be
missing:

      6.6 Per VLAN appointed forwarder status lost counter (see Section
          4.6.2).

The protocol draft doesn't seem to indicate how large this counter
needs to be (is 8 bits enough or would more be better?), but I think
this should be added into the existing "2.d VLANs and Bridge Roots"
sub-TLV.

-- 
James Carlson, Solaris Networking              <james.d.carlson at sun.com>
Sun Microsystems / 35 Network Drive        71.232W   Vox +1 781 442 2084
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