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ICMP: Destination unreachable (Protocol unreachable) from OSPF multicast

I have an IBM mainframe ("are they still mainframes?") that is generating an OSPF multicast. It receives a response "ICMP: Destination unreachable (Protocol unreachable)" for each OSPF multicast packet generated. The response comes back with a source address of (this address does not exist in my network). The mainframe is interfacing with my Cisco network which is fully OSPF operational and communicating with the mainframe without issue. But, this "unreachable" message is filling up the system logs. What can be causing this error message? Thanks.

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Re: ICMP: Destination unreachable (Protocol unreachable) from OS


Is there any indicator in the error message about what interface it was received on? I am wondering if the mainframe has some interface it is sending OSPF on that might not be connected to your router network. I believe that the protocol unreachable is consistent with receiving the OSPF packet on an interface that is not running OSPF. Since that address given is not in your network and since your network devices are running OSPF, it leads me to wonder if there is some interface connected to something else that might be generating these.



Re: ICMP: Destination unreachable (Protocol unreachable) from OS

Hello, I slightly doubt your statement, that is not in your network. If it would not be there, it couldn´t generate ICMP messages.

So there can be a couple of reasons. First, are there internal interfaces in the mainframe, which potentially have this IP?

What is the ARP cache on the main frame telling about Once you get the MAC you should be able to find the switch port or exclude this to be in your LAN switch environment.

Just a sidenote: This IP is widely used in small cable/DSL routers. Could there be a "rogue" router around?

Hope this helps! Please rate all posts.

Regards, Martin

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