Policy-based routing can be used to change the next hop IP address for traffic matching certain criteria. This can be useful to overrule your routing table for certain traffic types. I will show you how to configure policy based routing.
here’s the topology that we will use:
Take a look at the topology picture above. OSPF is configured on all routers. Since we are using Gigabit interfaces everywhere, traffic from R1 destined to 126.96.36.199 would normally be load balanced between R2 and R3. However, I changed the cost on the Gigabit Ethernet 0/3 interface of R1 so that all traffic will go from R1 > R2 > R4.
Want to try this for yourself? Here you will find the startup configuration of each device.
hostname H1 ! no ip routing ! no ip cef ! interface GigabitEthernet0/1 ip address 192.168.1.100 255.255.255.0 ! ip default-gateway 192.168.1.254 ! end
hostname R1 ! ip cef ! interface GigabitEthernet0/1 ip address 192.168.1.254 255.255.255.0 ! interface GigabitEthernet0/2 ip address 192.168.12.1 255.255.255.0 ! interface GigabitEthernet0/3 ip address 192.168.13.1 255.255.255.0 ip ospf cost 1000 ! router ospf 1 network 192.168.1.0 0.0.0.255 area 0 network 192.168.12.0 0.0.0.255 area 0 network 192.168.13.0 0.0.0.255 area 0 ! end
hostname R2 ! ip cef ! interface GigabitEthernet0/1 ip address 192.168.12.2 255.255.255.0 ! interface GigabitEthernet0/2 ip address 192.168.24.2 255.255.255.0 ! router ospf 1 network 192.168.12.0 0.0.0.255 area 0 network 192.168.24.0 0.0.0.255 area 0 ! end
hostname R3 ! ip cef ! interface GigabitEthernet0/0 no ip address ! interface GigabitEthernet0/1 ip address 192.168.13.3 255.255.255.0 ! interface GigabitEthernet0/2 ip address 192.168.34.3 255.255.255.0 ! router ospf 1 network 192.168.13.0 0.0.0.255 area 0 network 192.168.34.0 0.0.0.255 area 0 ! end
hostname R4 ! ip cef ! interface Loopback0 ip address 188.8.131.52 255.255.255.255 ! interface GigabitEthernet0/1 ip address 192.168.24.4 255.255.255.0 ! interface GigabitEthernet0/2 ip address 192.168.34.4 255.255.255.0 ! router ospf 1 network 184.108.40.206 0.0.0.0 area 0 network 192.168.24.0 0.0.0.255 area 0 network 192.168.34.0 0.0.0.255 area 0 ! end
Let’s verify this:
R1#show ip ospf interface GigabitEthernet 0/2 | include Cost: Process ID 1, Router ID 192.168.13.1, Network Type BROADCAST, Cost: 1
R1#show ip ospf interface GigabitEthernet 0/3 | include Cost: Process ID 1, Router ID 192.168.13.1, Network Type BROADCAST, Cost: 1000
Above you can see the increased cost. Let’s try a quick traceroute from H1:
H1#traceroute 220.127.116.11 probe 1 Type escape sequence to abort. Tracing the route to 18.104.22.168 VRF info: (vrf in name/id, vrf out name/id) 1 192.168.1.254 7 msec 2 192.168.12.2 6 msec 3 192.168.24.4 8 msec
Now let’s say I want to use the link between R1 and R3 to reach 22.214.171.124. I could influence the metric for OSPF, but this applies to all traffic. What if I wanted to use this link for certain traffic only?
We could use the link between R1/R2 for the majority of our traffic and use the link between R1/R3 only for certain traffic. This can be very useful. For example, imagine that the link between R1/R3 is a dedicated link that offers QoS for VoIP traffic.
This is something we can achieve with PBR (Policy Based Routing). Let me show you how!
Right now, all traffic is sent toward R2:
R1#show ip route | include 126.96.36.199 O 188.8.131.52 [110/3] via 192.168.12.2, 00:16:48, GigabitEthernet0/2
Now let’s say that we want all ICMP traffic from H1 destined for 184.108.40.206 to cross the link between R1/R3. Here’s how to do this:
R1(config)#ip access-list extended ICMP_H1 R1(config-ext-nacl)#permit icmp host 192.168.1.100 host 220.127.116.11
First, I create an access-list that matches my traffic. Now we have to create a route-map:
R1(config)#route-map PBR_H1 permit 10 R1(config-route-map)#match ip address ICMP_H1 R1(config-route-map)#set ip next-hop 192.168.13.3
Whenever the traffic matches the access-list, we will change the next hop to 192.168.13.3 (R3).
Last but not least, let’s activate it:
R1(config)#interface GigabitEthernet 0/1 R1(config-if)#ip policy route-map PBR_H1
Let’s see if it works. To see it in action, I will enable a debug on R1:
R1#debug ip policy Policy routing debugging is on
Now let’s send a ping from H1:
H1#ping 18.104.22.168 repeat 1 Type escape sequence to abort. Sending 1, 100-byte ICMP Echos to 22.214.171.124, timeout is 2 seconds: ! Success rate is 100 percent (1/1), round-trip min/avg/max = 13/13/13 ms
The ping is working. Let’s see what R1 thinks of it:
R1# IP: s=192.168.1.100 (GigabitEthernet0/1), d=126.96.36.199, len 100, FIB policy match IP: s=192.168.1.100 (GigabitEthernet0/1), d=188.8.131.52, len 100, PBR_H1 Counted IP: s=192.168.1.100 (GigabitEthernet0/1), d=184.108.40.206, g=192.168.13.3, len 100, FIB policy routed
Above, you can see that it has been policy routed towards 192.168.13.3. We can also verify this by looking at the route-map:
R1#show route-map PBR_H1 route-map PBR_H1, permit, sequence 10 Match clauses: ip address (access-lists): ICMP_H1 Set clauses: ip next-hop 192.168.13.3 Nexthop tracking current: 0.0.0.0 192.168.13.3, fib_nh:0,oce:0,status:0 Policy routing matches: 1 packets, 114 bytes
Let’s try some traffic that doesn’t match our access-list. Telnet, for example:
H1#telnet 220.127.116.11 Trying 18.104.22.168 ... Open
H1 can connect but it’s not policy routed:
R1# IP: s=192.168.1.100 (GigabitEthernet0/1), d=22.214.171.124, len 40, FIB policy rejected(no match) - normal forwarding
As you can see above, this telnet traffic is routed using the normal path.
There is one more thing I’d like to show you. With policy-based routing, there is a difference between traffic going through the router and traffic originating from the router.
The example above is for traffic that went through our router. What if we want to policy route traffic that originated from R1? We will have to use another command to activate it. Let’s create another route-map:
R1(config)#ip access-list extended ICMP_R1 R1(config-ext-nacl)#permit icmp host 192.168.12.1 host 126.96.36.199 R1(config-ext-nacl)#permit icmp host 192.168.13.1 host 188.8.131.52 R1(config)#route-map PBR_R1 permit 10 R1(config-route-map)#match ip address ICMP_R1 R1(config-route-map)#set ip next-hop 192.168.13.3
The route-map above will redirect all traffic from R1 to 184.108.40.206 toward R3. To activate this, we need to use another command:
R1(config)#ip local policy route-map PBR_R1
This time, we need to use the
ip local policy command. Let’s test this:
R1#ping 220.127.116.11 repeat 1 Type escape sequence to abort. Sending 1, 100-byte ICMP Echos to 18.104.22.168, timeout is 2 seconds: ! Success rate is 100 percent (1/1), round-trip min/avg/max = 19/19/19 ms
R1# IP: s=192.168.12.1 (local), d=22.214.171.124, len 100, policy match IP: route map PBR_R1, item 10, permit IP: s=192.168.12.1 (local), d=126.96.36.199 (GigabitEthernet0/3), len 100, policy routed IP: local to GigabitEthernet0/3 192.168.13.3
Great, our traffic from R1 is policy routed.
I tried to do the above lab; however been getting policy-rejected error.Below is the output... Continue reading in our forum
Your configuration looks ok, the strange thing is that the first packet matches but the second one doesn’t? What hardware are you using for this?
Here’s an example when I configure and debug it:... Continue reading in our forum
Hi Rene - I’ am on C2691-adventerprisek9-mz.124-25c let me know if you suggest for any other IOS.
Hmm that is one of the latest IOS images for that platform I think. You might want to try it on a 3725 in GNS3, that works for sure.
I have a question and it’s not in any of the subjects, maybe you can answer it.... Continue reading in our forum
I have a router with 2 interfaces:
G0/1–> ip address 172.16.254.6/30, G0/2–> 172.16.254.2/30, running OSPF. G0/1 Connects to my MASTER firewall with ip add 172.16.254.1/30 and G0/2 connects to my SECONDARY firewall with ip address 172.16.254.1, the firewalls are configure HA. If I try to configure G0/2 with an ip add of 172.16.254.3 it gives me an error. How can I make this scenario work with the 2 interfaces and the firewalls? or Do I need to get a switch module with 2 in