[c-nsp] IS-IS Topology database

[Oliver Boehmer (oboehmer)]

Mark Tinka <mailto:mtinka at globaltransit.net> wrote on Monday, September
29, 2008 7:51 AM:

> On Monday 29 September 2008 12:50:08 Oliver Boehmer
> (oboehmer) wrote:
> 
>> I've never really figured out what the backup routes in
>> ISIS are good for exactly (haven't digged deep into this
>> either), and I don't bother as you can achieve fast
>> convergence either way by tuning the SPF- and/or
>> PRC-interval down. So either topology is able to converge
>> equally fast.
> 
> In relation to this, I've posted (on my blog) IS-IS
> configurations I think are optimized for my environment
> (and perhaps, a few others):
> 
>
http://aknit-routing.blogspot.com/2008/06/is-is-routing-protocol-best-pr
actices.html
> 
> Feel free to gnaw at it and throw any comments.

a few comments after taking a quick look:

SPF and PRC-interval are quite aggressive. 1 msec initial wait is
appropriate for single link failures, but if you have multiple failures
within a short time frame (for example SRLG- or node-failures), you
might need to run two SPFs, so many deployments use 50ms initial wait. 
20 msec interval is quite low, some folks' SPF takes much longer than
this. So I would consider increasing this.
Same reasoning applies to lsp-gen-interval, for SRLG failures you might
need to generate two LSPs.

Not sure if I would consider "ignore-attached-bit" a Best Practice.. It
is useful in some environments, but many others would rely on it.

"log-adjacency-changes all" generates some more log files (for example
adjacency down when you shut an interface)..

AS you tune for fast convergence, "process-max-time 50" and "ip routing
protocol purge interface" (or "ip slow-converge" in non-12.0S/non-12.2S
trains) would also be recommended.

	oli