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Webcast-Catalyst9k
New Member

route filtering in IS-IS ?

Hello folks

i just notice that the distribute-list command is not avalible in isis. What would be the best solution to get rid of a certain route in isis ?

3 REPLIES
Purple

Re: route filtering in IS-IS ?

Hi,

With link-state protocols such as IS-IS, all routers within the same level have to have to same view of the link-state database. Therefore, the use of distribute-lists is not allowed since that would mean that the database would be different for different routers.

The only time you can do some filtering is when:

- redistributing external routes into ISIS

- using route leaking between L1 and L2 routers.

Hope that helps - pls do rate the post if it does.

Paresh

New Member

Re: route filtering in IS-IS ?

hi paresh

thanks a lot, you confirmed my assumtions. I was just wondering because in ospf this command is available. In my case i dont care if all my router have the unwanted prefix in the database, if i have the oppurtunity to filter it out between the database and the routing table

Purple

Re: route filtering in IS-IS ?

Hi,

As you mentioned, there is a rather subtle usage of the 'distribute-list in' command in OSPF. It will determine what routes get installed into the routing table of the router on which it is applied. The command can only be applied in an inbound direction. The use of this command in OSPF does not impact what gets advertised in the OSPF LSAs; it simply impacts what gets installed in the routing table.

Hope that helps - pls rate the post if it does.

Paresh

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