Subject: [rbridge] PS issue #11

From: spencer at mcsr-labs.org (Spencer Dawkins)
Date: Wed, 7 Dec 2005 14:51:04 -0600

I apologize for not sending mail on this issue when it confused me the first 
time...

Just to be clear (to me?), when we talk about

#11 internal/external, inside/outside terminology
    there is one objection to these terms as topological;
    the draft intends to define them sufficiently
    does this need to be addressed further?

In the following picture (constant-width fonts will help a lot on this), 
assume that "b"s are bridges, "r"s are rbridges, and "e"s are end stations. 
Are the set of bridges connecting to e1 part of the same spanning tree as 
the set of bridges connecting to e2?

e1 -- b --- b ----------- b
        \   |             |
          \ |             |
            b --- r ----- r
                  |       |
                  |       | (rbridge campus)
                  |       |
                  r ----- r -- b -- b
                  |               \ |
                  b --------------- b -- e2

In the following picture, are the (inside?) bridges in the middle of the 
rbridge campus part of the same (outside?) spanning tree, or does what 
happens inside the campus show up outside the campus?

e1 -- b --- b ---------- b
        \   |            |
          \ |            |
            b -- r --b-- r
                 | /   \ |
                 b ----- b (rbridge campus)
                 | \   / |
                 r --b-- r -- b -- b
                 |               \ |
                 b --------------- b -- e2

All clues are graciously accepted!

Thanks,

Spencer

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From: touch at ISI.EDU (Joe Touch)
Date: Wed, 07 Dec 2005 13:07:26 -0800

> the set of bridges connecting to e2?

That depends on TRANSPARENT, PARTICIPATE, or BLOCK. In BLOCK, e.g., no;
in TRANSPARENT, yes; in PARTICIPATE, that depends on the algorithm used
(i.e., there's a mode that Radia proposed - see ARCH ISSUE #3 - which
would be 'no', but in other cases it might be 'yes').

None of that affects this issue, though...

> happens inside the campus show up outside the campus?

The same issue applies - all bridges are 'outside'. It's only traffic
that's considered to be inside or outside. This is because the traffic
between rbridge nodes is tunneled, and it is the tunnel that is
'inside'. As a result, bridges may transit tunneled traffic, but they
never appear as bridges inside the tunnel, and so are never 'inside' the
rbridge.

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> rbridge at postel.org
> http://www.postel.org/mailman/listinfo/rbridge

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From: spencer at mcsr-labs.org (Spencer Dawkins)
Date: Wed, 7 Dec 2005 15:23:16 -0600

Hi, Joe,

Thanks for your help as I catch up ...

> never appear as bridges inside the tunnel, and so are never 'inside' the

I'm wondering if we have the potential for race conditions as bridges 
between rbridges recompute a spanning tree while rbridges are distributing 
link state updates, but at worst, I'm thinking this might involve one extra 
path change during routing changes - not oscillating. Maybe this is worth 
revisiting when we're more solid on the protocol description, but it's 
probably premature now.

Again, thanks!

Spencer

---

From: touch at ISI.EDU (Joe Touch)
Date: Wed, 07 Dec 2005 14:13:05 -0800

Spencer Dawkins wrote:
> link state updates,

There are cases in PARTICIPATE where that might matter, but in most
cases it should not, and it can't for TRANSPARENT or BLOCK. In any case
where the rbridge campus acts as a unit, it's not changing its
relationship to the edge trees even though it changes internally, so
there should be no race.

The only race would be when an rbridge device moves around within a
campus (unplug from one place and replug elsewhere), but in that case
there ought to be default rules about what to do until the trees on
either side (inside, outside) are stable.

?  but at worst, I'm thinking this might involve one extra