Policy based routing

This is more like a filter for networks. It has 3 basic steps

ACL to define interesting traffic
Routemap to refer to the ACL (If/Then statement)
Apply route Map to ingress interface

Normal traffic outward flow
R1 – R3 – R5 – R4 – R7
Return path
R7 – R4 – R5 – R3 – R1

Apply Route-Map on R4 to change the return Path
Return path

R7 – R4 – R3 – R1

R4# show access list

#access-list 100 permit ip host 7.7.7.7 any
#route-map PBR
#match IP address 100 // looking for Access list that matches acl 100. The “Match” is the “IF” portion
#set ip next-hop 10.34.0.3 //The “Set” is the “Then” portion
exit

//Please Note: If you do not specify a match statement, and only specify Set, it will match every other route to the PBR. If we dont set an alternative match statement, it will use the dedault route table.
//to check the route path

R7# traceroute 1.1.1.1
R7# traceroute 1.1.1.1 source 7.7.7.7

//to change the path, go to R4 ingress interface to apply the route map

R4# int se1/1.478
#ip policy route-map PBR

Verify the PBR you just applied

R4# sh ip policy
R4# Debug ip policy

// Lets go to R7
R7# traceroute 1.1.1.1
//Traffic flows normally as it is not coming from 7.7.7.7 but from 10.7.7.7
R7# traceroute 1.1.1.1 source 7.7.7.7
//Now you see the traffic path changes acording to PBR

Reference …From Keith Barker’s CBT.