Command to discover why router not fowarding packets?

[davidhvoss]

I have an odd situation where a router is receiving packets from a specific subnet but not forwarding it out the expected outgoing interface.  If I ping from Router 1 through Router 2 to the server, I can see that the server is receiving the ICMP packets and sending a response back through Router 2.  I see that Router 2 receives those packets but does not forward the packets over to Router 1.  Does anyone know a command (other than show int) where I can discover why these packets are being dropped?

ROUTER 1----------ROUTER 2--------SERVER

ICMP packets from Router 1 to server are received by the server but when the server responds back, Router 2 does not forward the packets to Router 1.

No ACL's are in place that would block the traffic.

I'm looking for a command to run to find out why these packets are being dropped.

[Richard Burts]

There are multiple things that might produce symptoms like this and I do not know of any simple command that will show you why the packets are dropped. Investigation of the problem is likely to have multiple steps and output from one step may guide toward the next appropriate step.

As a first question I would ask whether there are other devices on the subnet where the server is located and do you have the same issues with access to other addresses in that subnet?

As the next question I would ask whether the server (or other devices in that subnet) can ping or otherwise access addresses on Router 1?

And as the next question I would ask whether you can use extended ping from Router 2 to access the addresses on Router 1? In the extended ping specify the source address as the address of the router interface which connects to the subnet where the server is located.

Let us know the answers to these questions and we will see where it might take us.

HTH

Rick