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

[Jared Gillis]

On 06/23/2011 04:50 PM, David Barak wrote:
> Hi Jared,
> 
> You didn't specify this, so I'll hazard a guess that all of your NSAPs are in the same area, and that would cause the problem you're describing.  Routers that have NSAPs in the same area can form L1 relationships, and if they are in different areas they will not.

Yes, this is correct, currently the entire network uses the same NSAP format (42.<mac addr>.00).

> 
> Put each of your POPs in a different area, use a completely different area for your backbone routers, and the L1/L2 routers will set the ATT bit toward the L1-only POP routers, and you'll see the result you're looking for.  Remember, L2 will see everything, so the L1/L2 boundary needs to be thoughtfully chosen.  If you have a two-layer hierarchy, then the backbone itself are the L1/L2 routers (but each one is in a different area).  If you have a three-layer hierarchy, then L1/L2 belongs in the middle.
> 

So, if I'm reading your suggestion correctly, you're saying to have one isis area for the backbone (say with NSAP 42.<mac addr>.00), and a different area for each connected POP? 
Would the different area be created via a different instance (router isis pop1), or a different net address under the main isis instance? I may be getting confused between the different ways to segment an isis network, so I'm having trouble translating your suggestion to a config.

> Hope that helps,
> 
> David Barak
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