PBR is a packet routing and forwarding process that allows a router to determine how packets passing through it are handled based on a route map. The route map decides the next-hop forwarding router for a packet. Typically, enabling dynamic routing protocols on a router to dynamically learn the network topology may cause devices within the network to dynamically generate incorrect routing entries, leading to packet loss or packets being routed to the wrong destination. This is where we need to use PBR.
I. PBR is a packet routing and forwarding mechanism. By applying policy-based routing on a router, the router determines how packets passing through it are handled based on a route map, which decides the next-hop forwarding router for a packet.
II. To apply policy-based routing on a router, you must specify the route map used for the policy and create that route map. A route map consists of multiple policies, and each policy defines one or more matching rules and corresponding actions.
III. After an interface applies policy-based routing, all packets received on that interface are inspected. Packets that do not match any criteria defined in the route map are processed according to normal routing and forwarding. Packets that match a policy in the route map are processed according to the action defined in that policy.
IV. Suppose the E0/0 interface of a router serves as the gateway for the internal network with the address 200.1.1.1. The internal network has a web server with the address 200.1.1.100, and a user PC in the same network segment as the web server. There is a remote user in the external network with the IP address 199.1.1.100. The goal is to allow the remote user to access the web server but not the internal user’s PC.
V. Configuration
1. Router(config)#interface Ethernet0/0
2. Router(config-if)#ip address 200.1.1.1 255.255.255.0
3. Router(config-if)#exit
4. Router(config)#interface Ethernet0/1
5. Router(config-if)#ip address 199.1.1.1 255.255.255.0
6. Router(config-if)#exit.
VI. Route Map
1. Router(config)#route-map pbr
2. Router(config- route-map)#match ip address 100
3. Router(config- route-map)#set interface null