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

From: petera at nortel.com (Peter Ashwood-Smith)
Date: Mon, 17 Oct 2005 11:12:29 -0400

> >   Also, the 'problems' that people are attributing to 
> blocking and not 
> > processing BPDUs [BLOCK] are also 'problems' when no STP is running.
> 
> 'problems'? (why the quotes?)

  Because I don't see them and did not want people to think I did.
 
> OK, let's just shut off spanning tree in bridges and it all 
> works just fine now?
> 
> Now I'm *really* confused.

  Sorry, my explaination was not very clear. I was simply pointing out
that
the Rbridge DR mechanism avoids loops independently of the STP protocol.
Therefore, if there are no loops PRIOR to the introduction of the
rbridges
and their interconnections, but there is a loop AFTER their introduction
the
rbridges will detect and prevent it. In otherwords they detect and
prevent
loops for which they are responsible.

> If we want to say "BLOCK *MAY* work, but *MAY* silently 
> fail", and "PARTICIPATE and TRANSPARENT will always work with 
> current standards", that's fine (and, AFAICT, true), but I 
> also don't see how we pick BLOCK as a default in that case.

  I'd like to see the example of BLOCK failing and by failing I
mean a permanent loop uncorrected by either STP or Rbridge. Personally
I don't think this exists because the simple 'proof' of interconnecting
two
trees with a single link still being a tree seems pretty air tight to
me!

  Peter

---

From: touch at ISI.EDU (Joe Touch)
Date: Mon, 17 Oct 2005 20:18:35 -0700

> trees with a single link still being a tree seems pretty air tight to

Here's the counterexample:

Have existing bridges BLOCK.

Assume each bridge computes its own spanning tree internally (i.e.,
between its own ports on its own device), and sends coded 'hellos' that
it it recognizes if they loop, i.e., all the thinks a campus would do.

Now if that works, let's do it for bridges and then we wouldn't have a
spanning tree convergence problem at all, right?

If that does NOT work, then why does it work for rbridge campuses and
not bridges?

My general test is "an rbridge campus needs to look like a bridge" or
"look like a link". If it does, then I know I understand it. When it
doesn't, it would be useful to understand whether this is really a 'new
 animal' and exactly why it's newness is unique to rbridges (i.e., why
it can't be applied as well to bridges).

Joe
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