[rbridge] VLAN registration

[Caitlin Bestler]

I think we need to de-couple TRILL compliance from any specific
level of 802.1 compliance on any specific 802.1 cloud/protocol suite.

802.1 is in the process of defining various "clouds", such as
Data Center (for Congestion Notification and other purposes)
and AVB (audio-vide-bridging). The issue of where an RBridge
should or even can extend those clouds is complex, and a rat
hold best avoided by allowing implementers to do as litte or
as much as they want and only dealing with issues that affect
RBridge functionality.

Participation in any of these clouds should clearly be optional
(as in MAY). The draft should be clear that 802.1 documents will
describe RBridge interactions with conventional bridges. Those
documents already protect the right of end stations and bridges
to upgrade or  not upgrade at their own pace.

That suggests the only extent to which TRILL needs to be involved
is to allow a mechanism by which two RBridges can communicate their
intent to extend a specific 802.1 cloud through the RBridge tunnel.
Even that can be worked around. To the extent that standard signaling
is required I think it can be added in later documents as additional
TLVs in the discovery process.

I certainly hope that RBridge functionality is considered as a 
superset of Bridge functionality, and not as an excuse for freezing
Bridge features at a certain revision. But it's up to the market to
determine which 802.1 protocols are relevant, not IETF.