Subject: Re: [Isis-wg] too many segments

From: Radia Perlman - Boston Center for Networking <[email-masked]>
Date: Mon, 12 Jun 2000 11:22:49 -0400 (EDT)

Mike,

I didn't quite understand your paragraph 
>>>we could fail to detect the path through the 
>>>pseudonode, because the destination node would already have been added to 
>>>PATHs and we can't (don't) increment the adjacency set of node already on 
>>>PATHS.

But as for your worry about having zero cost loops, I'd think you wouldn't
need to have the cost be zero in both directions. For instance, suppose
the node that has too much LSP information to fit into 255
fragments is named "A". So A invents new nodes A',
A'', A'''. A adds neighbors A', A'', and A''' to its LSP as neighbors with
zero cost. A also creates LSPs from A', A'', and A''' with the excess LSP
info that didn't fit into the LSP for A, and also each with neighbor A with
reasonably large, but finite cost.

Would that work, and then eliminate any possible implementation confusion
with zero cost loops?

Radya   ;-)

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From: Mike Shand <[email-masked]>
Date: Mon, 12 Jun 2000 16:38:21 +0100

>Would that work, and then eliminate any possible implementation confusion

I don't think that works in all cases. If the information in A', A'' etc's 
LSPs are just leaf information, then its fine, but if you had lots of 
genuine router adjacencies, then I think the two way connectivity check 
gets you. A' has links to B,C etc. These are real costs. But if we have 
links from B to A', C to A', then you end up needing to use the A' to A 
link to compute a route through A. You can't do the obvious thing of making 
B link directly to A, since then the two way check would get you since 
there was no link from A to B.

Am I making any sense?

I admit that the most likely reason for LSP size explosion is lots of 
imported routes, for which your solution would work fine.

         Mike