IP Routing Tables with OSPF Troubleshoot

[mabarian86]

Hi all,

The scenario attached works fine with OSPFv2 activated in R1, R2 and R4 and advertising all the networks. Then I decided to disable OSPF in R4 and introduce a static route in R2 as follows:

Router2# ip route 172.16.10.0 255.255.255.0 10.1.1.1

This way, when R2 wants to ping R4, it will address to R1 first. Then, let's look at R1's routing table:

Router1#show ip route
Gateway of last resort is not set

10.0.0.0/24 is subnetted, 1 subnets
C 10.1.1.0 is directly connected, FastEthernet0/0
 172.16.0.0/24 is subnetted, 1 subnets
C 172.16.10.0 is directly connected, Serial0/0

So, when R1 wants to forward the ping to 172.16.10.2, he knows that he must send it over the serial0/0 interface because the routing table says so (last line). Unexpectedly (by me), something strange happens. The ping dies at some point between R1 and R4. I say it is strange, because a ping from R2 to 172.16.10.1 does work, but a ping to 172.16.10.2 does not work. What could be the problem here?

[Jon Marshall · Accepted solution]

R4 does not have a route back to the 10.1.1.x subnet because you turned off OSPF on it.

Jon

[mabarian86]

Wow, that was... so easy it was embarrasing. I need a rest definitely. I added a static route from R4 back to R2 and of course it works now.

Thank you very much Jon!

[Jon Marshall]

No problem, glad to help.

Jon