RIPv2 - Manipulation of the Metric with Offset Lists

Lets take a lab of 2 routers and do some basic RIPv2 configuration:

Both routers just have the interface serial 1/0 and the interface loopback 0 configured. If you use the basic RIPv2 configuration and start the routers you can ping the other router.

The routing table of R1:

Two more loopback interfaces are added to R2. The routes have an administrative distance of 120 and a metric of "1", which basically is a hop count. This value has a range of 1 to 15.

R2#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R2(config)#interface loopback 10
R2(config-if)#ip address 172.17.0.10 255.255.255.255
R2(config-if)#exit
R2(config)#interface loopback 20
R2(config-if)#ip address 172.17.0.20 255.255.255.255
R2(config-if)#end

R1#show ip route
Gateway of last resort is not set

     172.17.0.0/32 is subnetted, 4 subnets
R       172.17.0.20 [120/1] via 192.168.100.2, 00:00:05, Serial1/0
R       172.17.0.10 [120/1] via 192.168.100.2, 00:00:05, Serial1/0
C       172.17.0.1 is directly connected, Loopback0
R       172.17.0.2 [120/1] via 192.168.100.2, 00:00:05, Serial1/0
     192.168.100.0/30 is subnetted, 1 subnets
C       192.168.100.0 is directly connected, Serial1/0

The two new routes now appear in the routing table of router R1. The metric of RIP routes can be manipulated with offset lists. For this to work an accesslist has to be configured. The metric of 172.17.0.10 will be increased by 5 on router R1 incoming on the interface S1/0, the metric of 172.17.0.20 will be increased by 7 outgoing on router R2.

R1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)#access-list 10 permit 172.17.0.10 0.0.0.0
R1(config)#router rip
R1(config-router)#offset-list 10 in 5 Serial 1/0
R1(config-router)#end

R2#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R2(config)#access-list 20 permit 172.17.0.20 0.0.0.0
R2(config)#router rip
R2(config-router)#offset-list 20 out 7 Serial 1/0
R2(config-router)#end

R1#show ip route
Gateway of last resort is not set

     172.17.0.0/32 is subnetted, 4 subnets
R       172.17.0.20 [120/8] via 192.168.100.2, 00:00:00, Serial1/0
R       172.17.0.10 [120/6] via 192.168.100.2, 00:00:00, Serial1/0
C       172.17.0.1 is directly connected, Loopback0
R       172.17.0.2 [120/1] via 192.168.100.2, 00:00:00, Serial1/0
     192.168.100.0/30 is subnetted, 1 subnets
C       192.168.100.0 is directly connected, Serial1/0

Save this configuration, it will be used as a base for other tutorials on this website. The configuration for this tutorial can be downloaded from here.