EIGRP neighbor-multicast problem

[patrick.lopez]

I have an existing WAN network that has been in production and working for over two years.

In a isolated part of the network there are three routers connected via Ethernet on a 2900 series router. Each of the routers has a serial connection to a different remote location.

We are using eigrp as the routing protocol.

Recently we introduced a layer 2 Ethernet connection that is being handed off to us by an outside vendor for Internet connectivity. All I have is an RJ45 cable that I plug into the switch.

I have no idea what kind of equipment it plugs into at the other end.

The problem is as follows:

Whenever I connect the new Ethernet hand off to the 2900 switch the three routers lose their EIGRP neighbor relationship in a matter of minutes..

Each router can still see its neighbor across the serail link but none of them can see each other across the Ethernet segment on the 2900 switch.

As soon as I unplug the new connection, within seconds the neighbors reestablish themselves.

When the new layer 2 link is connected and the routers lose their neighbor relationship I cannot ping the 224.0.0.10 address but I can unicast ping all addresses.

When I unplug the link I can ping the 224.0.0.10 no problem.

I have checked spanning tree with and without the new connection and do not see any obvious problems.

I have been in contact with the vender but they really have not been very helpful.

Any insight, comments or suggestions would be much appreciated.

Thanks

Pat

[gmarogi]

I am not sure what is happening exactly. You can try couple of things to get some clue. Probably you can try to use some of the eigrp debugging commands like 'debug eigrp packet' or 'debug ip eigrp neighbor' command to see what is happening. You may be able to see some difference in the debugs when the new Ethernet is connected and disconnected. You can also try looking at the CAM table entries on the 2900 switch to see if there is any difference with and without the ethernet connection. Another thing that you can try is connecting a network analyzer tool and capturing the packets and analysing them.

[rjackson]

The new remote must have a router on the same ip net as your routers are using on the switch with an address that you gave them. You must have also given them an address to be their next hop to reach the internet. It sounds like they got it backwards and are using the next hop as their routers address. When you plug them in they are taking over the address of one of your routers.

Check the arp tables of all of the routers addresses on the switched lan before you plug them in. Plug them in ,ping around and check the arp tables again. See if the mac addresses in the tables change. Use the mac-address table to figure out where the addresses in the arp table plug into the switch.

[patrick.lopez]

Looks like it has something to do with IGMP.

If we turn off IGMP snooping on the switch the problem goes away.

Pat