[rbridge] Time to summarize "forward or block" BPDU thread

[Joe Touch]

Radia.Perlman at sun.com wrote:
> It works perfectly well if RBridges block. It isolates the bridge islands.
> 
> Routers also block bridge spanning tree, and to exactly the same
> effect as if RBridges block BPDUs.

This isn't the same at all; I keep hearing the analogy, but it fails
under all tests:

	first, there are NO routers on an L2 net

	all sources/sinks are the same (called nodes AFAICT)
	and hosts and routers are just nodes,
	identical as far as L2 is concerned

	nodes block all BPDUs (we agree), but
	nodes also block broadcast (rbridges don't)

Near as I can tell, L2 has exactly three devices currently:

	nodes

	links

	bridges (participate in SPT, interpret BPDUs)

Bridges don't 'block' BPDUs, but they don't forward them to all ports
either.

Now, an rbridge can be "like" a node, a link, or a bridge and still play
in the existing L2 specs. If it isn't 'like' any of those, then we're
changing the definition of 802, and I didn't think that was the goal here.

rbridges - at least to nodes on the L2 - are NOT 'like' hosts, since
they don't source or sink L2 traffic to existing nodes

rbridges could be 'like' links if they are TRANSPARENT

rbridges could be 'like' bridges if the PARTICIPATE

What exactly are rbridges 'like' if they BLOCK?

They can't be 'like' routers - there are no routers in L2.

??

Joe
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