[rbridge] Discovering endnodes directly connected to an RBridge

[Joe Touch]

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Joe Touch wrote:
> 
> 
> Saikat Ray wrote:
> 
>>>I am not sure how Joe is defining "campus". The page 3 of the draft says "A
>>>campus refers to a set of links connected by either RBridges or bridges. In
>>>other words, the campus is terminated by traditional IP routers." 
> 
> 
> Yeah - that seems like a bug. It seems like an rbridge campus is a set
> of links connecting either bridges or rbridges, terminated by rbridges.
> 
> i.e.,
> 	rbridges connected to internal bridges or rbridges
> 	internal bridges connected to internal bridges or rbridges
> 	all external links connected to rbridges only
> 		(declare these 'edge' rbridges')
> 	all nodes (hosts) connected via the external links
> 
> But there don't need to be IP routers per se.
> 
> Joe


FWIW, I did clarify this with Radia off-line. Rbridges campuses are
terminated at the rbridge, largely because of an IP router or host, but
it is at the rbridge that the termination exists.

As to the above,, here's a clarified version:

There are three kinds of L2 devices in an rbridge:

	hosts: anything that sources/sinks L2 packets
		e.g., RFC1122-style hosts, RFC1812-style routers
		(routers act like hosts to L2)

	bridges: transit conventional L2 packets and source/sink/transit
		spanning tree messages

	rbridges: encapsulate/decapsulate L2 packets with shim/L2 hdrs
		exchange routing via IS-IS,
		exchange egress tables via some protocol (TBD)

host-host and host-rbridge traffic
	may transit bridges
	is conventional L2

	this is known as EXTERNAL TRAFFIC

rbridge-rbridge traffic
	may transit bridges (since it looks like L2 on the outside)
	is shim/L2 encapsulated

	this is known as INTERNAL TRAFFIC

I hope this helps; it's a preview of the architecture doc ;-)

Joe
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