Policy Routing

Policy Based Routing is a technique used to make routing and forwarding decisions based on user-defined policies set forth by access-lists, packet size or other criteria.

For Example:

• R1 has a default route pointing to the Ethernet link connecting to R3.
• R2 has a default route pointing to the Ethernet link connecting to R3.
• R4 has a default route pointing to the serial point-to-point link to R3.
• R5 has a default route pointing to R3 out the Frame-relay. 
• R4 has a static route to R5's loopback.
• R5 has a static route to R4's loopback.

Here we see that R3 does not have routing information for either Loopbacks of R5 or R4:

So R3 cannot send traffic there when it is locally generated:

Let's implement Policy Based Routing (PBR) on R3:

1. Configure the extended ACL.
2. Configure Route-Map.
3. Apply the Route-Map under the incoming interface using the ip policy command. 

Configure the ACL:

Configure the Route-Map:

Apply the Route-Map under the incoming interface using the ip policy command:

VERIFICATION:
If traffic comes in from R1 or R2's IP address attached to Ethernet network, it is routed according to the route-map attached to the incoming Fa0/0 interface.

Traceroute to R5's Loopback and R4's Loopback:

On R3, debug ip policy: