EIGRP Review

The morning started with a review of EIGRP. I haven't considered EIGRP for quite some time and don't work with it daily, so a review is good.

EIGRP is a relatively simple protocol to configure from a basic level. With a few simple commands, it can be enabled on a router and will likely run without issue. All it takes is a "router eigrp" with an autonomous system number and a network command and away it goes.

router eigrp 1

network 10.0.0.0

Normally we'd want to add a wild card mask to the network statement, but when a statement like the above is entered, it will enable EIGRP on all interfaces that match the classful IP address in the network statement. If the wild card mask is added, it will apply ACL properties to apply EIGRP only on the interfaces which match the mask.

Commands for verifying the functionality of EIGRP would then be:

show ip interfaces This command shows which interfaces EIGRP is enabled on and routing, omits passive interfaces

show ip protocols Shows which protocols are in effect and which networks are being advertised, or rather the contents of the 'network' commands as well as a list of neighbor IPs

show ip eigrp neighbors Lists the routers who have established relationships with the router on which one is currently working, and does not list neighbors for which a mismatched parameter prevents a valid EIGRP neighbor relationship

show ip eigrp topology shows the topology table, including the successor, feasible successor route, but does not list all known topology details

show ip route Lists all the networks for which this router is aware, including details of how the route was learned (by which protocol, connected, etc) and the administrative distances. All EIGRP-learned routes are labelled with a 'D'

I spent some time reacquainting myself with these commands last night, and was glad to see that with a little effort, I'm able to hone in on the information needed to troubleshoot and resolve any issues. I was also glad to make a mistake in my EIGRP test lab, where I misconfigured an interface. When I added the network to my EIGRP ASN, the route did not propagate. It ended up that the network I added didn't contain the IP address of the interface, and therefore EIGRP knew that there was no information to send to its neighbors. Using 'show ip eigrp int' I was able to see that it was not enabled on all the interfaces for the router. I was then able to troubleshoot backward and see where my mistake had been made.

A good review for the night. I'll continue reviewing tomorrow.