[c-nsp] Unified MPLS - Discrete area or separate IGP in Access Layer

[Mark Tinka]

On Thursday, February 06, 2014 05:25:49 PM Adam Vitkovsky 
wrote:

> And I did support this. However now facing real world
> restrictions of 12K routes per ME (app template) or
> ASR901 I could probably use some separation for future
> proofing the network.

Practically, when you run L1/L2 levels, you end up having to 
do Route Leaking (i.e., redistribute L2 into L1), meaning 
you come off with the same number of routes as you had 
before going multi-level.

You could summarize L2 routes and redistribute those into 
L1, but you end up with sub-optimal routing (which is why I 
recommend turning off the ATT bit when doing L1/L2 routing 
anyway).

> Way back when I haven't had any major problems with
> inter-area or inter-as MPLS-TE, or MVPN for that matter
> -but that wasn't on ME :).

You can use expanded loose hops to string an LSP across IGP 
level domains, but it adds complexity.

Also, p2mp RSVP-TE didn't support expanded loose hops until 
now (well, there is an I-D that I saw going around).

> So ISIS L2 everywhere though Edge and Metro-E Access
> rings are not continuous L2 but rather separate domains
> interconnected with BGP-LS please?
> 
> -Which I would now accomplish with RFC3107 in the
> meantime.

Right, although I'm not sure BGP-LS will buy you FIB space 
savings, as the idea is, really, to redistribute IGP routing 
across a BGP domain. So you get scaling due to avoiding IGP-
style messages, but not sure you save much on actual routes.

But then again, because it's BGP, you should be able to 
apply filtering to limit what gets into the FIB, so yes, it 
could work.

Mark.
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