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

[Justin Shore]

Jared Gillis wrote:
> In this configuration, routers A and B learn all routes in the network, and exchange them via their L2 link.
> Routers C and D are only aware of their directly connected routes, plus a default towards A/B. C does not have Ds routes, and vice-versa, however they are able to ping each other's loops, by following default to A/B which do have the route towards the loop.
> I have also taken down the mesh-style connection between A/D and B/C, so the network looks like:
> C---A---B---D
> And the design works exactly the same.
> When I replace A with a 7204VXR running 12.2 SR ipservices, the whole thing breaks. C has no default towards A, and B does not learn any routes that C advertises to A.

This is why we were forced to deploy a flat L2-only topology on our 
network.  We could not get multiarea IS-IS for IP to work on our 7600s 
running 12.2SR.  Since it works on the hardware in your example with the 
7200s and simply doesn't work because of the code that I personally call 
that a bug that needs to be squashed.  I would open a TAC case and 
approach it from that angle.  The only reason it doesn't work is because 
it hasn't been coded in 12.2SR.

> The design constraint I have is that in my production network, the C/D routers will be 3750s, which do not have the TCAM space to learn every route in the network I am building, and they will always be a stub (or more exactly an OSPF TS-NSSA), so that's the behavior I am looking for.
> I could move to OSPF, but this network will utilize MPLS, and I want to use the MPLS TE extensions of IS-IS. I am aware that OSPF has similar extensions, but IS-IS works better for us, and the network is already built on IS-IS, and an IGP migration is something I'd like to avoid if possible.

I was going to through up a red flag about trying to run IS-IS on a 3750 
because the last time I looked fixed-config non-ME Cat switches didn't 
support IS-IS.  However I checked the FN just to be sure since it's been 
a long while since I looked and sure enough they added IS-IS to the 
3750s with 12.2(50)SE.  You did mention MPLS though so I'll go ahead and 
bite at that one.  Are you planning on running MPLS on your 3750? 
You're wording doesn't specify one way or another.

Justin