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Community Member

OSPF route filtering

Hi All

 

I am trying to filter all routes apart from the default route out of an incoming OSPF update.  I have managed to make this work by using a distribute list inbound on the interface where the default route comes from, and I thought all was fine. 

However when I look at a downsteam OSPF router, all of the routes I blocked are still there. I think this is because the LSA still contains the routes, and the distribute list only works on the local router.

Is there any way I can filter so that only the default route is accepted into the router, and other routers downstream. I think I need to filter outbound on an interface if possible

Any ideas please? - its driving me mad

Cheers

Russ

5 REPLIES
VIP Purple

HelloYou don't state how this

Hello

You don't state how this ospf domain is setup - are all rtrs in the backbone area 0 or are you trying to filter between areas?

Can you post your config?

 

res

Paul

 

Please don't forget to rate any posts that have been helpful. Thanks.
Community Member

Hi Paul All routers are in

Hi Paul

 

All routers are in area 0. Its a little tricky to post the complete configs, but I can post some snips if needed

Cheers

Russ

VIP Purple

HelloOkay can you post a

Hello

Okay can you post a small topology diagram to show the physical setup of the ospf domain showing the interface types and then maybe also

sh ip ospf neigbours
sh ip ospf route

 

 

res

Paul

 

Please don't forget to rate any posts that have been helpful. Thanks.
Community Member

If all routers are in area 0,

If all routers are in area 0, you will have to use the distribute list on all the routers.

If the other routes were coming from another area, as well as the default route, you could use a prefix list on the border router to stop the additional routes from entering area 0.

Hall of Fame Super Gold

Russ did a pretty good job of

Russ did a pretty good job of analyzing his own problem when he says "I think this is because the LSA still contains the routes, and the distribute list only works on the local router". It is an important distinction that a distribute list filters what routes are put into the routing table but can not filter the advertisements in the LSA.

 

If Russ wants to suppress all of the learned routes other than the default then he would have to configure the distribute list on all of the routers i the area. Or he can choose a different routing protocol. If your network design is based on being able to filter out some learned routes then a protocol like EIGRP is generally a better choice since it does allow filtering of routing advertisements at any point in the network that you might choose.

 

HTH

 

Rick

 

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