[c-nsp] How to effect a totally stubby area in IS-IS

[David Barak]

--- On Thu, 6/23/11, Jared Gillis <jared.a.gillis at gmail.com> wrote:

> Okay, I see what this is doing. I set this up in the lab,
> and it worked as you described, however, if I have two POPs
> connected to one BB router, both POP routers see each
> other's L1 announcements (I assume because they are in the
> same area). This config should limit the "leaked" routes to
> only other POPs directly connected to the same BB, but we
> really need to get the POPs to only ever receive default, as
> we've got upwards of 30 POPs connecting to each BB router.
> Also, to throw another monkey wrench in the works, each POP
> is redundantly homed off two BBs, so it would learn double
> the number of prefixes learned by the POP.
> 
> Here's a quick diagram of what the network needs to look
> like:
> BB1---BB2
> |\     /|
> | \   / |
> \  POP1 /
>  \     /
>   \   /
>    POP2
> 
> The BBs should be learn all routes in the network (L2), and
> the POPs can be whatever level, but they should only learn
> default, ever.
> 

That type of topology will be problematic in this context - if BB1 and BB2 are in different areas, then POP1 and POP2 would both be single-homed.  If they're in the same area, then POP1 will see POP2's routes.  If the POPs are L1/L2, they'll definitely see each other's routes.  Would it work to use ISIS for just the loopbacks and interfaces, and then carry all of the other routes in BGP?

Alternatively, you could add more routers to the topology so that they could stay dual-homed in a single area, but that can be expensive depending on the platform.

David Barak
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