[c-nsp] IS-IS route separation/filtering

[Jared Gillis]

Hello all,

I'm trying to accomplish something with an IS-IS network, and I'm starting to
think it may not be possible, but I'm hoping someone here might have a
suggestion to help.
Basically, what I'm trying to accomplish is to have two routers subtended off an
aggregation router. So, say Router A has a link to Router B and Router C. I want
Router A to advertise a default route to B and C (this I have done), and B and C
should announce their routes to A (also done), but I do *not* want B to learn
C's routes, nor C to learn B's. This is my sticking point.
Currently my config is that A is L1/L2 and B and C are L1 only, but since they
are all in the same area, they learn all of each other's routes.
I could put B and C into different areas, and put A into both of those areas as
well, but I need to have up to 15-20 L1 routers hung off of Router A, and all
the docs say that you can only configure 3 NET addresses on a Cisco router, so
this won't scale to what I need.

Basically I'm trying to replicate the concept of an OSPF
totally-stubby-not-so-stubby-area in IS-IS, and I'm starting to question whether
it can be done. My network design is fairly flexible at this point (the only
requirements are that it run IS-IS and L1 routers don't learn each other's
routes), so I'm open to any ideas or suggestions.

Thanks for your time

-Jared