Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

BGP case

Hi All,

Look at this scenario:

networkB -------->R1 -------->R2 ----->internet (normal flow)

networkA --------> \--------> R3 ----->internet

R1 is connected to R2 and R3.

Networks A and B are connected to R1 and have route to R2 and then

Internet.(normal flow),all the links are iBGP.

There are cases where I want that networkA will take different path,

means via R3 (for limited time,I want to control it)

I want that R3 will do the new advertisement when i want to change the normal flow of the traffic sourced from net A. My concept is to make a BGP advertisement that will trigger some rules/routes in R1 (like the sinkhole solution of Cisco under DDOS attack) and cause the packets from net A to pass via R3.

Some minor configs on R1 are possible but the main config/advertisement


will do.

In your answer please forget PBR (no ip policy on interfaces but

route-map are


I'm searching for BGP tricks to do it.(tags are also possible)

The main problem here that legacy routing works on destination (which in


case is unknown/internet) and here I have to decide based on the source without PBR.

net A and B relationship is not an issue.

Any ideas ??



Re: BGP case


Are you receiving, full internet routes on your routers ?

Do you want your policy to be automatically trigerred, or manually by yourself?

If you want to reroute the traffic via, R3, manually, you can manipulate the BGP local preference parameter for all outgoing updates via IBGP to neighbor R1.

(I believe you have a full mesh IBGP session between, R1,R2 and R3).

A route-map can be used to manipulate local preference attribute. If you want to manually control it, you will need to take on/off the route-map applied on R3, to neighbor R1.

New Member

Re: BGP case


Thanks for your answer.

I want that the process will be as mach as it can be automatically.

The Internet routes are not issue here. The main things is about Routing principles want that only traffic from net A will take different path not all the updates from R1.As I know the local preference will do it to all updates.

Because the basic routing algorithm is working based on destination the only module/process that I know that can route based on source is PBR.Do you know anything else?


CreatePlease login to create content