The Lazy Networker

In this topology we are using RIPv2 and R2 is getting route information about 10.4.4.0/24 from R3 and R1. But i don’t want to install two routes in the table. I want to use R3 to reach that network for that  i am using Offset-List.

Lets check the present routing table of R2

10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
R 10.4.4.0/24 [120/2] via 172.16.23.1, 00:00:20, Serial1/1
                        [120/2] via 172.16.12.1, 00:00:28, Serial1/0
172.16.0.0/16 is variably subnetted, 6 subnets, 2 masks
R 172.16.14.0/30 [120/1] via 172.16.12.1, 00:00:28, Serial1/0
R 172.16.34.0/30 [120/1] via 172.16.23.1, 00:00:20, Serial1/1

R2#show ip route 10.4.4.0
Routing entry for 10.4.4.0/24
Known via “rip”, distance 120, metric 2
Redistributing via rip
Last update from 172.16.12.1 on Serial1/0, 00:00:00 ago
Routing Descriptor Blocks:
* 172.16.23.1, from 172.16.23.1, 00:00:20 ago, via Serial1/1
Route metric is 2, traffic share count is 1
172.16.12.1, from 172.16.12.1, 00:00:00 ago, via Serial1/0
Route metric is 2, traffic share count is 1

Offset-List Configuration
!
access-list 1 permit 10.4.4.0
!
router rip
version 2
offset-list 1 in 14 Serial1/0
network 10.0.0.0
network 172.16.0.0
no auto-summary
!

Now we can see that only one route is present in routing table

10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
R 10.4.4.0/24 [120/2] via 172.16.23.1, 00:00:07, Serial1/1
172.16.0.0/16 is variably subnetted, 6 subnets, 2 masks
R 172.16.14.0/30 [120/1] via 172.16.12.1, 00:00:09, Serial1/0
R 172.16.34.0/30 [120/1] via 172.16.23.1, 00:00:07, Serial1/1

If we debug RIP updates we can see that one route is inaccessible because of maximum hop count rule in RIP.

*Sep 21 18:06:49.248: RIP: received v2 update from 172.16.12.1 on Serial1/0
*Sep 21 18:06:49.248: 10.4.4.0/24 via 0.0.0.0 in 16 hops (inaccessible)
*Sep 21 18:06:49.248: 172.16.14.0/30 via 0.0.0.0 in 1 hops
*Sep 21 18:06:49.248: 172.16.34.0/30 via 0.0.0.0 in 2 hops