[c-nsp] IS-IS Multiarea on 12.2 SR

[Jared Gillis]

Mikael Abrahamsson wrote:
> In order to detect loopbacks going away and using this to
> invalidate/remove next-hops quickly, you can't aggregate anyway.
> 
> Sorry, I have yet to hear someone describe an ISP network (designed as
> per ISP essentials, carry loopbacks in IGP and everything else in BGP),
> where IGP aggregation makes sense. If you have 10k routers in your IGP,
> well, you most likely did something wrong earlier in the process.
> 
> Also, with modern processorns and techniques such as partial tree
> recalculation in modern router OSes, I'm sure even 10k routers would be
> manageable in a single area.

While I agree with these statements, our issue is not tree recalculation/convergence. Our issue and driving need for IS-IS multiarea is the fact that we have 3750ME's which can only hold ~2k routes in the TCAM in our IS-IS domain, and we'll very rapidly exhaust the TCAM unless we can do route summarization (i.e. upstream L2's send default/ATT only).

-Jared