isis route summarization

[epelser_2]

Hi

I have a router (Rtr-A) connected to an ATM link. I also have the following connections to Rtr-A:

Rtr-B (level-1 router) on S0/0.100

Rtr-C (level-1 and 2 router) on S0/0.110

The routes I'm summarizing are 196.5.128-131.0/24 into a single route of 196.5.128.0/22 using the level-1-2 option

When I look at the routing tables on Rtr-B, I still see all 4 subnet (/24 mask) but on Rtr-C I'm seeing the summarized routes and the 4 subnets.

Is there any way to only see the summarization through simply using the summary command or will I have to utilize route maps?

[Georg Pauwen · Accepted solution]

Hello,

AFAIK, ISIS route summarization can only occur between areas and between levels. Is your Router B a level 1 router and in the same area as your Router A ? That would explain why you do not see the summary route at all on Router B. Check the same on Router C, it could be that you see the summary route as a level 2 route, and the 4 subnets as level 1 routes...

Just a thought.

Regards,

GP

[epelser_2]

Hi

Rtr-A & C are level-1 & 2 routers. Rtr-B is only level 1. I have not restricted the link between A & C to a particular level. I'm seeing the summarization as L2. All three routers are also in the same area.

I'm studying for my CCIE lab exam so would it be possible to email me directly at ernst.pelser@infosecureltd.com

Thanks

[Harold Ritter · Accepted solution]

First, I would like to start by saying, hwat a scenario!! Only in the CCIE lab you'll see something like this (hopefully) ;o)

Rtr-B sees the 4 /24 prefixes via the level-1 LSP.

Rtr-C also sees the 4 /24 prefixes via the level-1 LSP and the /22 via the level-2 LSP coming from Rtr-A.

In this scenario, the only way you could see only the summary on Rtr-B and C is to redistribute these 4 subnets into isis instead of configuring isis on the interface(s) where these addresses are configured and do the summarization as you redistribute into isis.

I suppose Rtr-A is the one originating these prefixes. Right?

Hope this helps,