[rbridge] Consensus Check: Announcing Root

[Eastlake III Donald-LDE008]

This is a check via the mailing list on a slight modification of an
apparent consensus from the minutes of the Chicago meeting for a change
from protocol draft -05. The tentative consensus at the Chicago meeting
was:

   It is mandatory for an RBridge to announce the bridge root that
   it sees out each physical port.

Based on mailing list discussion, I would like to tweak this as follows:

   An Rbridge MUST parse BPDUs it receives on a port and announce
   in the core IS-IS instance the bridge root that it sees out
   each port. For MSTP (Multiple Spanning Tree Protocol), this is
   the CIST (Common and Internal Spanning Tree) root.

I have a question in connection with this. What is announced for the
port if no BPDU has been received recently or ever? Should there be a
"root MAC address valid" flag per port or should there some conventional
value, like zero, which is announced?

Thanks,
Donald