How to debug route issue on Cisco 2921

[rene.kockisch]

There is a cisco 2921 and two Networks are connected. On GigabitEthernet 0/1 there is the 10.1.10.0/24 networks connected and on GigabitEthernet0/0 there is the network 10.1.11.8/30 connected. The router has the IP configured gi0/1 with 10.1.10.11 and gi0/0 with 10.1.11.9 this works, on route I can ping both interfaces and all clients available in the networks. But if I'am outside of the router on a client 10.1.10.100 connected on gi0/1 over a switch. I can ping to both interfaces of the router but cant reach the Client in the network attached on gi0/0. Is there any policy with an ACL or do I have an issue in my router config.

Output of sh ip route

Gateway of last resort is 10.1.10.1 to network 0.0.0.0
S* 0.0.0.0/0 [1/0] via 10.1.10.1
 10.0.0.0/8 is variably subnetted, 4 subnets, 3 masks
C 10.1.10.0/24 is directly connected, GigabitEthernet0/1
L 10.1.10.11/32 is directly connected, GigabitEthernet0/1
C 10.1.11.8/30 is directly connected, GigabitEthernet0/0
L 10.1.11.9/32 is directly connected, GigabitEthernet0/0

I also set a ip route 10.1.11.8 255.255.255.252 GigabitEthernet0/0 but that also doesnt solve my issue. I cant ping the client in the 10.1.11.8 network outside the router. Ping from client 10.1.10.100 to 10.1.11.9 works but for 10.1.11.10 it doesnt work.Is it possible that the client 10.1.11.10 has the wrong route added? I cant check because this client is not accessible for me. I will be sure that isnt a issue on my config, so I need a way to debug what is wrong. Maybe if the 10.1.11.10 is configured without a route to 10.1.11.8/30 with gateway 10.1.11.9 it can be possible but I'am not sure for this.

[Richard Burts · Accepted solution]

Based on the symptoms that you describe the most likely explanation is that the client at 10.1.11.10 does not have a route to the 10.1.10.0 network. There is a simple way to test this. You have told us whether the router is able to ping the client at 10.1.11.10. So I would start with that: can the router ping the client at 10.1.11.10? If it can not then there is an issue about the client at 10.1.11.10 and you need to investigate why it does not respond to ping. Perhaps it has firewall rules that does not permit ping?

Assuming that the router does successfully ping the client at 10.1.11.10 then we know that the client will respond to a ping. The next step is to use extended ping on the router. In the extended ping you would specify the destination of 10.1.11.10 and you would specify that the source is 10.1.10.11. If the client does not respond to this then it is pretty clear that the client does not have a route for this network.

HTH

Rick

[rene.kockisch]

Hey Rick,

thx a lot, with the extended ping I cant reach the client so the route is not configured on the Client. The extended Ping is the right way to debug this. Thx.

[Richard Burts]

I am glad that my answer was helpful. Thank you for using the rating system to mark this question as answered. This will help other readers in the forum to identify discussions that have helpful information. These forums are excellent places to learn about Cisco networking. I hope to see you continue to be active in the forum.

HTH

Rick