PBR

General Notes

  • Conditional forwarding of packets based on something other than destination IP
  • Possible filters include source IP, source & destination IP, protocol type (TCP, UDP, ICMP)
  • Downsides are operational complexity, increased load on router
  • Can specify multiple next-hops - when done the first will be used if the next-hop is adjacent, otherwise it will use the second, third, etc
  • If you want to use a non-adjacent route, you must use the recursive flag when configuring the route-map set statement
  • Using the default flag will cause the next-hop value to be set only for routes not within the router’s RIB
  • Can also combine PBR with IP SLA & Tracking to ensure reachability of next-hops
  • Local PBR
    • This is a PBR for traffic sourcing from the router (normally not subject to policy routing)
    • Configuration is the same as a typical PBR but applied with ip local policy route-map <rm-name>

Useful show/debug commands

  • show ip policy - Show PBR details
  • show ip local policy - Show local PBR details
  • debug ip policy - Shows policy-based decisions in real time

Standard PBR Config

ip access-list extended AL_PBR
 permit ip 10.1.1.0 0.0.0.255 10.5.5.0 0.0.0.255
!
route-map RM_PBR-TRANSIT permit 10
 match ip address ACL-PBR
 set ip [default] next-hop 10.23.1.3 <optional second IP>
!
interface GigabitEthernet0/1
 ip policy route-map PBR-TRANSIT

PBR with IP SLA & Tracking Config

ip sla 1
icmp-echo 10.3.3.2
ip sla schedule 1 life forever start-time now
!
track 1 ip sla 1 reachability
!
ip access-list standard ACL
 permit ip 10.2.2.0/24 10.1.1.1/32
!
route-map PBR
 match ip address ACL
 set ip next-hop verify-availability 10.3.3.2 track 1
!
interface GigabitEthernet0/1
 ip policy route-map PBR-TRANSIT