[rbridge] How many trees, and per what

[Alia Atlas]

Sanjay,

On 10/27/06, Sanjay Sane (sanjays) <sanjays at cisco.com> wrote:
> Also, instead of adding F-tag "values" to the context of the Rbridge-id,
> why not treat "F-tag" as the Forwarding topology identifier. (quote from
> http://www.ietf.org/internet-drafts/draft-gai-perlman-trill-encap-00.txt
> --> "The Forwarding Tag (FTag) identifies the forwarding topology
> assigned to a given frame").
>
> In the tree usage case (unknowns/multicast/broadcast), it's the tree
> identifier. If flood/unknown packets are best sent using ingress-rbridge
> tree, use the F-tag of the tree rooted at that ingress rbridge. If
> multicast packets are best sent using shared-multicast trees, use the
> F-tag of the (load-balanced) shared tree.
>
> Again, which tree/topology the packet is to be put onto, is the decision
> made at the source/ingress rbridge. But once the tree is chosen, and the
> F-tag is put on the packet, other rbridges honor the F-tag and forward
> accordingly.

Why have a separate additional field for this purpose?  The only
meaning of the ingress rbridge nickname in the shim header is, I
believe, to indicate the intended multicast tree.   Could the shared
multicast trees be given a nickname from the same space?  This would
avoid the need for the additional overhead and change in the header.
Are there scalability considerations that would make this a problem?

Alia