Policy-Based Routing (PBR) allows network administrators to override the default routing behavior and specify how traffic should be routed based on matching criteria. PBR uses route-maps to match packets and set the next-hop. Route-maps contain match and set clauses - match clauses define the conditions to match packets, and set clauses define the action to take for matched packets such as specifying the next-hop router. Network administrators configure PBR by defining route-maps with match and set statements, applying the route-map to an interface with the ip policy command.

1. Policy-Based Routing (PBR)

2. Content
- Before We Start
- PBR Overview
- How PBR Works
- Route-Map Operation
- PBR Configuration Procedure
- PBR Configuration - Lab

3. Before We Start
- Destination Based Routing
- Routing from Net A/B to
Net C/D via (R1 -> R5 -> R4)

4. PBR Overview
- Say goodbye to Destination Based Routing
- Flexible routing packet decision based on traffic
flows
- Overrides routing protocol next-hob decision

5. PBR Overview
- Routing from Net A to
Net C via (R1 -> R5 -> R4)
- Routing from Net B to
Net D via (R1 -> R2 -> R3 -> R4)

6. How PBR Works
- All packets received on an interface are
considered for policy
routing
- Each packet is passed through a route-map
- Each entry in a route-map has “match” and “set”
clauses
- Match clauses are conditions to be met
- Route-map is used for condition work

7. How PBR Works
If match src NetA
set next-hob -> R5
If match src NetB
set next-hob -> R2

8. Route-Map Operation
route-map DEMO permit 10
match X Y Z
match A
set B
set C
route-map DEMO permit 20
match Q
set R
route-map DEMO permit 30
If {(X OR Y OR Z)
AND A match}
Then {Set B AND C}
(and exit route-map)
Else
If Q matches
Then set R (and exit route-map)
Else
Set nothing (and exit route-map)
OR
OR

9. Route-Map Operation
- Match criteria on the same line mean a logical
OR condition
- Multiple match and set criteria on separate lines
indicates an AND condition
- A route-map statement without any match
statements will be considered matched.
- Like an access list, an implicit deny any appears
at the end of a route map.

10. PBR Configuration Procedure
- Define and name the route map with the route-map
command.
- Define the conditions to match (the match
statements).
- Define access-list for packet identifying
- Define the action to be taken when there is a
match (the set statements).
- Define which interface the route map will be
attached to using the ip policy route-map interface
configuration command.

11. PBR Configuration - Lab

12. PBR Configuration – Lab
Configuration on R1
- Create access-list
ip access-list extended Net7-Net4
permit ip 7.7.7.0 0.0.0.255 4.4.4.0 0.0.0.255
!

13. PBR Configuration – Lab
Configuration on R1
- Configure route-map
route-map DEMO permit 10
match ip address Net7-Net4
set ip next-hop 192.168.12.2
!
route-map DEMO permit 20
!

14. PBR Configuration – Lab
Configuration on R1
- Apply route-map into interface
interface FastEthernet6/0
ip policy route-map DEMO
!

15. PBR Configuration – Lab
Traceroute output from Network 7.7.7.7
- Before Apply into interface
traceroute 4.4.4.4 source 7.7.7.7
Type escape sequence to abort.
Tracing the route to 4.4.4.4
1 192.168.16.1 20 msec 12 msec 12 msec (R1)
2 192.168.15.5 12 msec 36 msec 28 msec (R5)

16. PBR Configuration – Lab
Traceroute output from Network 7.7.7.7
- After Apply into interface
traceroute 4.4.4.4 source 7.7.7.7
Type escape sequence to abort.
Tracing the route to 4.4.4.4
1 192.168.16.1 12 msec 20 msec 20 msec (R1)
2 192.168.12.2 30 msec * 34 msec (R2)
3 192.168.23.3 32 msec * 36 msec (R3)
4 192.168.34.4 68 msec 56 msec 52 msec (R4)
5 192.168.45.5 56 msec 68 msec 60 msec

17. Thanks