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Community Member

Specific Routes from the BackBone Router

Hi All,

Can anyone please tell me how to go about how ONLY a specific routes should be allowed from the BB routers?, i.e. R1 should not accept any routes from BB1 that have an odd number in the first octet.

Please help me!!!!!!!

4 REPLIES
Community Member

Re: Specific Routes from the BackBone Router

Sorry,

I'm not exactly sure what the question is.

Hall of Fame Super Gold

Re: Specific Routes from the BackBone Router

I agree that the question is not clear. It seems to be asking how to limit the routes that are learned from the backbone router. But it is possible that the question is really about how to limit the traffic that is sent from the backbone router. Perhaps the original poster can clarify this?

Assuming that the question is about how to limit the routes that are learned and assuming that there is a dynamic routing protocol like EIGRP or RIP (note that this approach does not work with OSPF as you would expect it to) running from the backbone router, then the solution would be to configure a distribute list under the routing protocol. The distribute list would use an access list which would deny any route whose first octet is an odd number and would permit all other routes. It might look something like this:

distribute-list 1 in

access-list 1 deny 1.0.0.0 254.255.255.255

access-list 1 permit any

HTH

Rick

Community Member

Re: Specific Routes from the BackBone Router

Rick,

I am most grateful for your help as usual. Sorry if my question is not clear enough even though you have partly answered my question.

The question is that i have only one link to a Backbone router, which i do not know what routes it's housing but i should not allow any route with ODD number in the first octet.

Going by your answer, what has indicated that the first octet with odd number is blocked?, it is the 1 in the access-list?

I just hoped my question is clearer this time?.

Thank you

Hall of Fame Super Gold

Re: Specific Routes from the BackBone Router

I am glad that I was able to infer what your question was really about. I hoped that it was fairly clear that what indicated that the first octet with odd number is blocked is that the access list statement says to deny any route that matches the condition of the wildcard and IP address. The wildcard of 254.25.255.255 says to only check the low order bit of the first octet and if that bit contains 1 then deny. And any route with 1 in the low order bit of the first octet is an odd value.

HTH

Rick

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