I have a multi-homed network setup. I'm using a Cisco 7200 to do BGP advertising to both provider A and B. For each provider, I have a separate /24 that I'm using. I am AS prepending to influence the block A to provider A, and block B to provider B. This works fine. If either provider goes down, failover works great.
However, I also want to influence OUTBOUND traffic to flow to each provider in the same way. That is, as traffic comes in my router, I want to associate its outflow to the provider based on the source IP address. As is, each provider advertises to me just a default route.
I believe I can use routing policy to achieve this, but I don't want to hardcode the IP addresses in the policy since they could change dynamically.
So, what are my options to influence the outbound routing?