EIGRP Routing on a Cisco 3550

This evening I was trying to get a Cisco 3550 switch (EMI) to form an EIGRP adjacency with a router directly connected to it. However, I kept getting the following syslog message:

%DUAL-5-NBRCHANGE: EIGRP-IPv4 10: Neighbor 172.26.6.9 (GigabitEthernet0/0) is down: retry limit exceeded

... and the ip route command showed nothing. Same with show eigrp neighbor and topology command. So what was going on?

Router neighbors

I ran the debugs on both the router and switch, and that showed me nothing.  I checked all manor of protocol settings, rebooted both devices, checked CPU usage etc.

I could ping the router from the switch and vice versa, so what was I doing wrong?

I had missed one vitally important step when using L3 capability on a switch; I had neglected to enable the routing.

As soon as I issued the command ip routing, my neighbor adjacencies came up and my route tables now held the correct shared routes.

So, what was it that tipped me off? I was checking to see if the switch was enabled to handle multicast traffic. Now this is important because the EIGRP routing updates are multicast. The way to do this is to type:

(config)# ip m?

and you will see the multicast commands listed. I did not see that, in fact I saw nothing. So I backed up a little and typed:

(config)# ip ?

and as I was scrolling through the list of possibilities, I saw, routing ... and my memory was jogged.

Sometimes you just have to remember the basics!