ODR----filtering the default route

Unanswered Question
Jun 19th, 2007

I have ODR configured on hub router but I don't want the hub to send the default route to a certain neighbor.

I tried "passive-interface" and "distribute-list" commands under router config mode for ODR and it doesn't work.

My guess is since ODR uses CDP these features won't work for this protocol.

Do I need to disable CDP all together between these two routers?

I want to filter the CDP advertisement but I'm not sure if this is possible.

Thank you

I have this problem too.
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2pparish Wed, 06/20/2007 - 05:47

Thanks Satish, that link was good but not exactly what I was looking for.

I don't think there is a way to block the default route from being "pushed" or advertised to stub routers without disabling CDP.


Edison Ortiz Wed, 06/20/2007 - 06:57

Is the neighbor running other routing protocols ?

What's the reason for not wanting the default route on this neighbor ?

You can blackhole the default route with a static route pointing to null0 in the neighbor router, that is if you don't want to disable CDP between devices.

2pparish Wed, 06/20/2007 - 10:12

This is strictly experimental so I'm testing ODR and different configurations.

The blackhole sounds like a good idea.

Would I just add this command on the neighboring router

ip route null0

I need to take this default route from the hub out of the RIB(routing table).

Could I create a default route on the neighbor with a lower AD and point this route towards somewhere else. The neighbor is a transit router thats the problem, not a stub router.

This is all experimental of course.

Thank you

Edison Ortiz Wed, 06/20/2007 - 10:59

ODR is meant for stub routers at the spokes. If you have a transit router at one of the spokes, you will have to bring another routing protocol into the mix or rely on static routing, quite messy.

2pparish Wed, 06/20/2007 - 11:19

Actually the config I was doing was kind of neat.

I have 1 hub, 3 spokes, and a transit router connected to the hub.

What I plan on doing is using RIPv2 or OSPF on the hub and transit router. and then redistribute ODR into the IGP. The reason I wanted to get rid of the defaul route is I don't want the transit router sending default traffic back to the hub.

I'm going to create a static default route on the transit router with a lower AD then the ODR advertised default. This should knock the ODR route out of the RIB, or maybe not.

Thank you

Edison Ortiz Wed, 06/20/2007 - 11:32

The hub should be the only router running

'router odr'

the spokes will learn only the default route and the hub will learn all connected routes from the spokes (yes, you can also add redistribution into the mix).

The spoke (on this case the transit router) will never send a default route to the hub via odr. The spoke should never have the router odr statement on it.

A static route will automatically blackhole the ODR route or any other dynamic route.

2pparish Wed, 06/20/2007 - 11:38

You got it right.

I blackholed the ODR route and it worked.

I was hoping there was some way to prohibit that route from making it to the transit router but it looks like filtering CDP advertisements is not part of a Cisco router toolset.

Thanks for your help.


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