[c-nsp] Reasons for "random" ISIS flapping?

[Mark Tinka]

On Wednesday, August 07, 2013 11:55:11 AM Peter Rathlev 
wrote:

> We only have one area and should actually be using L2
> only. We hadn't thought it through when we decided on L1
> many years ago. I'm thinking that L1 only or L2 only is
> better than L1+L2 everywhere and the only practical
> drawback of using L1 seems to be the inability to inject
> a default route. Any other gotchas we should be worrying
> about?

L1-only requires that the Area ID of the NET be the same, 
otherwise adjacencies won't form. 

L2-only doesn't have this issue, although operationally, you 
might want to come up with some kind of protocol for how 
Area ID's in the NET are assigned.

That said, RSVP-TE has inter-area issues, which can 
complicate features that require it to run, e.g., NG-MVPN, 
MPLS-TE, e.t.c. So sticking with a single level is probably 
a good idea. IS-IS scales well, anyway, and even though 
there might be added noise by going with one level, the 
benefits compensate for that.

Perhaps, in the long term, SR can make inter-area TE 
simpler.

Mark.
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