Subject: [rbridge] IS-IS Level and TRILL Question

From: "David Michael Bond" <[email-masked]>
Date: Fri, 24 Jul 2009 12:03:27 -0400

Hello Everyone,
I had a question regarding IS-IS and TRILL. My apologies if this has been
brought up in the past.

Recently the follow comment was made:
       Perhaps the first sentence in Section 4.2.3 ("All Rbridges must
participate in the TRILL IS-IS instance.") should have "which constitutes a
single Level 1 IS-IS area using the fixed area-ID zero" appended to it.

My question is, is there anything preventing layer 2 TRILL IS-IS from being
configured as multiple level domain such as layer 3 IS-IS? This would break
"zero configuration" but if some campus wished to have this additional
control is there any reason why this could not be done? I also realize that
TRILL is not meant to be any larger than existing layer 2 networks. So there
might not be the desire for that additional control.

Thanks,
David

~~~~~~~~~~~
David Bond
Research and Development, Routing
InterOperability Laboratory, University of New Hampshire

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From: Radia Perlman <[email-masked]>
Date: Sat, 25 Jul 2009 21:10:02 -0700

I like David's suggested wording. It is a clarification.

As for whether we'd ever want mulilevel TRILL...I'm not sure how 
valuable multilevel TRILL
would be since I think the nicknames have to be globally unique within 
the entire TRILL campus and there's
no ability to aggregate endnode learning. So it's possible that a campus 
would run out of nicknames, or
get overrun with unknown destination flooding or ARPs, long before there 
would be any benefit of
moving to multiple levels of hierarchy.

Radia