Subject: [rbridge] Is it a problem to limit to 255, the # of links R1 can be DRB for?

From: Radia Perlman <[email-masked]>
Date: Tue, 05 May 2009 10:07:59 -0700

As Mike Shand pointed out, the IS-IS spec really does say that the 7 
byte pseudonode ID
has to have the top 6 bytes=system ID of the DR.

So what would break if that was simply ignored? There are two ways that 
the restriction
is used today in IS-IS:

a) In the IS-IS spec (as Mike pointed out), it helps R1 recognize a 
pseudonode
LSP that R1 had generated in a previous incarnation (before R1 crashed), 
so R1
knows it should purge it
b) for general manageability, so it's clear which router generated 
pseudonode ID "R1.x"

So...it seems like there are several choices at this point for TRILL:

1) assume the 255 link limit is not a problem, especially with pseudonode
suppression, and keep the restriction that the 7-byte pseudonode ID has
to have the top 6 bytes=the DRB's system ID

2) say that the top 6 bytes can be any 6-byte ID owned by the DRB, which
still allows it to recognize its own LSPs, and makes the # of links it 
can be
DRB for pretty much unlimited (it probably has a MAC address for
each of its links)

3) allow the multicast form of the system ID (where the multicast
bit is set), in addition to the regular system ID, which doubles the
number of links R1 can be DRB for (and declare a pseudonode for)

4) change the format of LSP to have 8 byte IDs  rather than 7.

Radia

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From: James Carlson <[email-masked]>
Date: Tue, 5 May 2009 13:49:53 -0400

> 4) change the format of LSP to have 8 byte IDs  rather than 7.

Both (1) and (2) sound good to me.  (2) sounds fairly familiar.
(Likely something we did back at IronBridge ...)

I'm not sure I see a point for (3) over (2).  As long as you're using
something other than 'the' system ID, what you choose to use likely
has no additional impact.  Thus, trying to keep the address "similar"
by making just one bit different probably isn't helpful.

I wouldn't want to see (4) unless it were changed everywhere.  Keeping
a hack like that straight for just TRILL IS-IS would be difficult.

-- 
James Carlson, Solaris Networking              <[email-masked]>
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From: Donald Eastlake <[email-masked]>
Date: Sun, 10 May 2009 21:32:40 -0400

I think it would be good to allow for more than 255 links and I support
option 2. I also agree with Mike Shand that, for ease of debugging, that
option shouldn't be used unless necessary.
Thanks,
Donald
=============================
Donald E. Eastlake 3rd   +1-508-634-2066 (home)
155 Beaver Street
Milford, MA 01757 USA
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From: mike shand <[email-masked]>
Date: Tue, 12 May 2009 11:34:39 +0100

Donald Eastlake wrote:

I think it would be good to allow for more than 255 links
and I support option 2. I also agree with Mike Shand that, for ease of
debugging, that option shouldn't be used unless necessary.

Yes, I think the simplest thing is to assume its not a problem, but
allow 2 if it turns out that it is. This isn't really a technical
change, just the removal of a restriction.

Option 4 is an unnecessarily large change.

Mike

Thanks,

Donald

155 Beaver Street

Milford, MA 01757 USA

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On Tue, May 5, 2009 at 1:49 PM, James
Carlson <[email-masked]>
wrote:

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