What is it?
- A technique to send transit traffic out of an AS using the shortest path with the goal of reduction in transit traffic
How it is done?
- MED and Hot Potatoes are normally exclusive to each other. Reset MED from another AS, and use IGP best path to route traffic out to another AS
RR and Hot Potato Routing
- When RR is present, hot potato routing is broken. Because RR only reflect one BEST path, from its perspective. That may not be the best path for the PE perspective.
- The solution is to use UNIQUE RD for MPLS VPN, or ADDITIONAL PATH
What feature we need to enable ADDITIONAL PATH?
- Enable BGP multipath in ingress PE so the PE can store multiple paths in its RIB
- That is all you need if you use iBGP full mesh.
- If you have MPLS VPNv4, you can use unique RD
- However if you have RR, the RR needs to have ADD-PATH feature enable
- If you modify local preference to make a PE the preferred egress route, you need to enable “BGP BEST EXTERNAL” so that additional external route will be advertise via iBGP