[rbridge] it's time to summarize things
touch at ISI.EDU
Wed Dec 14 21:33:38 PST 2005
Radia Perlman wrote:
> I just got back from a bunch of travel, and was trying to catch
> up on the mailing list, and it's really so long.
> It looks like the thread of whether RBridges participate
> in spanning tree popped up again. I thought that had been
> RBridges should NOT participate in spanning tree, which means
> they should DROP spanning tree messages.
> An RBridge should NOT merge spanning trees. It should terminate
> spanning trees, just like routers do.
I'm one of the ones confused by the use of routers as an analog.
Routers terminate L2 broadcasts. Rbridges cannot. Routers decrement L3
TTLs. Rbridges cannot. So the assertion that an rbridge campus should
drop BPDUs - just like routers - doesn't follow.
So at the very least we need to explain the reason for this behavior
more clearly, in a way that does not refer to routers as equivalent.
AFAICT, having an rbridge campus drop BPDUs makes sense only by
effectively considering the rbridge campus as the root of all trees, but
that presumes it is always _the_ root (that there is only one 'drops
BPDU' system per bridged LAN). Since there's no way to enforce that
assertion, it seems problematic.
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