Subject: Re: [Isis-wg] BCP for building Integrated IS-IS Network

From: Danny McPherson <[email-masked]>
Date: Thu, 13 Jan 2000 19:33:20 -0700

I agree with Henk's comments.  

We run a single area L2-only domain with a couple hundred routers, other 
places I've worked had 350+ in a single domain.  The primary reasons for not 
introducing hierarchy are those Henk mentioned:

o Inability to derive accurate BGP MED values  
o L1 routers defaulting to closest L2 router can result in sub-optimal routing.
o Troubleshooting is a bit more complex

The ability to route leak does make a multi-level IS-IS network more 
appealing, though it's certainly not worth the complexity trade-offs at this 
point, or anywhere in the foreseeable future.

I didn't see Henk mention it, but it would perhaps also seem that while a 
multi-level network is a bit more protected against potential of instabilities 
introduced by link oscillation, a single level network should converge 
slightly faster, though the gain is probably negligible.

As for the SPF runtimes, they don't seem at all concerning in our network 
today.  We use two different vendor implementations and SPF runtimes seem to 
be ~200 microseconds per node.  We don't have any NBMA stuff or psuedonodes 
though, so the size of the LSDB is probably pretty small in comparison to 
other networks.

-danny

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From: Ran Atkinson <[email-masked]>
Date: Fri, 14 Jan 2000 11:08:52 -0500

IMHO, the analyses in recent emails (e.g. Henk's) would
be useful to document in a short Informational RFC.

Ran
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