Fundamental EIGRP Commands

The theory behind fundamental EIGRP concepts is useful, but an engineer (or aspiring CCNP) must also know how to configure and verify EIGRP on Cisco IOS by using a few key commands.  This post will discuss several of the most common commands and what they are typically used for.

The first command, show ip protocols, gives a fairly long output:

show ip protocols

While lengthy, this command displays a considerable amount of information that is useful for an engineer who is troubleshooting EIGRP networks.  It shows which interfaces are passive – in this case, fa0/0 and fa0/1 – and displays the K-values used to calculate the EIGRP metric weight.  It also displays all information entered via the network command.

Another long but useful command is show ip route. This command produces the following result:

show ip route

This command, like the previous one, is obviously not limited to just EIGRP.  It shows all routes  in the routing table – whether connected, static, EIGRP, OSPF, or other – and the associated interfaces.  EIGRP routes are coded as “D”.  In the picture above, the router has only been configured with EIGRP; all other routes are “C” for direct connections learned by the ip address x.x.x.x y.y.y.y interface command.

The next commands are EIGRP-specific. First up is show ip eigrp interfaces. This command displays the interfaces which have EIGRP enabled (actively – passive interfaces are not listed), and how may peers are known through each interface.

show ip eigrp interfaces

Fairly simple!  However, if we want to know a little more about one of the interfaces displayed here, we can append detail and the interface name to the command to result in the following output:

show ip eigrp interfaces detail serial1-1

This command gives us the Hello and Hold timer information configured for a particular interface (only Hello is displayed in the output above due to an outdated router IOS version), as well as statistics about EIGRP messages sent and received.

While we would use the previous command, show ip eigrp interfaces detail s1/1, to display the Hello and Hold timers advertised by the router for one of its interfaces, what would we use to show the current Hold timer for a given neighbor router?  They key word is “neighbor” – that information would come from the next command, show ip eigrp neighbors.

show ip eigrp neighbors

This command shows valid neighbors, the interfaces used to reach each neighbor, and the current (live) hold timer for each neighbor, but how do we know if the neighbor relationship was discovered dynamically or set statically?  An addition to the command, show ip eigrp neighbors detail, provides that information:

show ip eigrp neighbors detail

This output (from router R2, which has a discovered neighbor relationship with R1 and a configured neighbor with R3 via s1/0) shows a the “static neighbor” line directly below the relevant IP address.

And finally, show ip eigrp topology shows us information about the EIGRP ASN, the router ID, and successors and feasible successors, which will be discussed in a later post.

show ip eigrp topology


Back to IOS

After spending two years in Information Assurance and cybersecurity policy, it’s time for me to get reacquainted with the core routing and switching technologies that enable modern network security concepts.  What better way to restart my networking studies than by pursuing another Cisco certification?  And that’s the train of thought that ended with an Amazon Prime delivery of the Official Certification Guides for 300-101 (ROUTE) and 300-115 (SWITCH).  These books are just a little heavier than my CCNA texts, and I’ll be using real IOS images with GNS3 instead of Packet Tracer emulation on this go-around, but the learning process should be the same (if a bit rusty).

The first few chapters of the ROUTE Official Certification Guide (OCG) were largely reviews of basic CCNA topics such as IPv6, network design, and basic routing protocols.  Chapter 4 introduced fundamental EIGRP concepts such as neighbor relationships and EIGRP verification commands.  The lab topology was simple – just three routers with serial interconnections and five subnets connected via fast ethernet ports – and the configuration commands were equally simple.

Fundamental EIGRP Topology

Setting up EIGRP is almost trivial:

router eigrp 1

This quick three-line snippet is all that is needed to run EIGRP on all R1 interfaces: Fa0/0, S1/0, and S1/1 (in the classful class-A network) and Fa0/1 (in the classful class-C network). Adding a wildcard mask such as after the IP address in the network statement allows for more elegant deployment of EIGRP by classless subnets rather than classful A/B/C networks.

Finally, the chapter reintroduced five key EIGRP verification commands – show ip eigrp interfaces, show ip protocols, show ip eigrp neighbors, show ip eigrp topology, and show ip route. Each of these commands displays a different set of information about the EIGRP configuration, including hello and hold timers, passive interfaces, and metric weights (K-values).

None of the material in this chapter was earthshatteringly new or complex, but I will definitely need to commit the verification commands to memory – if my previous experiences are any guide, show run will not be an option on the ROUTE exam!