BGP- Difficulty with NULL0 Route

[alliancebroadbandkolkata]

Hello

We are a small ISP with links from two larger upstreams.

Take for example , I am advertising 192.168.52.0 / 22 IP Block through ISP1. For this I am putting a Null0 route " ip route 192.168.52.0 255.255.252.0 Null0 " . One of the router's interface is assigned with the IP address 192.168.52.1 /22 - whole customer network is running through that interface.So far so good.

Now I want to introduce ISP2 & advertise only 192.168.52.0/24 IP Block through ISP2. This I cant - the Block is not getting advertised unless and until I add the route " ip route 192.168.52.0 255.255.255.0 Null0 " & as soon as I add this route the interface on which the IP address 192.168.52.1 /22 is assigned stops pinging- and it is turning to a mess.

Any suggestion to how to advertise only the 192.168.52.0/24 block through ISP2 .

Please revert if any clarification is needed.

Abhishek

[Rick Morris]

I understand that part but if there is already a ip route in there for the /22 would not the prefix list then use the /24 because of the le 24 at the end of it?

[Jon Marshall]

Rick

I may be misunderstanding what you are getting at but it must be an exact match ie. the network and the subnet mask before it can be advertised.

Jon

[Richard Burts]

Jon

And that is why I suggested that he not use a null 0 static route but use a static route specifying the outbound interface with the specific prefix and subnet mask that he wants.

Something like this:

ip route 192.168.52.0 255.255.255.0 gig0/12

HTH

Rick

[Jon Marshall]

Rick Burts

"And that is why I suggested that he not use a null 0 static route but use a static route specifying the outbound interface with the specific prefix and subnet mask that he wants."

Yes i realise that. I totally agree with you.

Think you mistook my last post to Rick ie the other Rick (engagerocks), as addressed to you :-).

Jon

[Richard Burts]

Jon

My apologies. You are correct that I did not realize that there were 2 Rick active in the thread. Thanks for helping me realize this. Your comment to the other Rick now makes sense.

HTH

Rick

[Rick Morris]

I stand corrected.

I was thinking in reference to permitting and or denying incoming traffic on specific announcements using the le command.

Sorry to muddy up the water

[yagnesh_tel]

Jon/Rick B.

Perhaps my understanding of BGP inject map is wrong but isn't that can be used in this case as you already have aggregate route and you want to inject more specific route?

[alliancebroadbandkolkata]

Yagnesh -

I have checked BGP Inject Maps with cisco docs- it may be possible by inject-maps , but the feature is available only with some specific hardaware/software platforms.I need to depend upon traditional methods available.

All-

Lets do it & monitor it for sometime. I will update you with feedbacks.

Abhishek

[Jon Marshall]

Yagnesh

I've never used this feature but from the looks of it your understanding is perfectly correct, this would indeed be another solution to the same problem.

Jon

[alliancebroadbandkolkata]

All-

The settings are working ok , it is running for the last 3-4 days I have not registered any problems.

Thanks to all.

Abhishek