Troubleshooting EIGRP

Preparing the CCNA is being challenging, troubleshooting just guessing is consuming time, besides you get quicker results if you define some steps about how to proceed. This is the procedure I will normally follow if something is not working properly.

1. Checking the interfaces are in UP/UP state

Before starting with routing protocols, verify the interfaces are working properly

R1> show ip int brief

2. Checking L2

Review if there is any problem on the serial link:

3. EIGRP neighbors and AS

Confirm that you have the expected neighbors, besides examine the AS is the same in all the routers.

R1> show ip eigrp neighbor

4. EIGRP interfaces

It may occur that either some interfaces are not enabled or there are some interfaces enabled with a wrong network command.

R1> show ip eigrp interface

If there is some interface that is enabled (from the previous step), but neighbors routers do not see that network, review the configuration. Regarding a network command, review the command itself or the wilcard.

i.e: network (but you actually have
i.e: network (actually you want for /30)

R1> show ip protocols 

The above command will show if there is any error, with the network definition. If the network command for that interface was not added, it will not appear.

5. K-values and passive interfaces

Actually, we can get the next information from the previous check, however I think is much clear to review it aside.

R1> show ip protocols 

This command shows you any passive-interface, what it would actually avoid to establish neighbor relationships. Remember that K-values must match on both routers, you can check the values using the previous command as well.

R1(config-router)# no passive-interface s0/0/0

6. EIGRP Authentication

I’m not sure if this topic is covered for the CCNA, however is for sure one of the issues you may find. In this case, configuring:

The previous parameters must agree when setting up EIGRP authentication.

If Frame Relay is configured on a physical interface, broadcast will not be supported, the same occurs for point-to-multipoint links. Define subinterfaces or modify the ospf network type.

In multipoint networks add the broadcast keyword at the end. The show frame-relay map shuld show broadcast, otherwise it will not work.

R1(config-if)# frame-relay map ip <IPADDRESS> <DLCI> broadcast

8. Access lists filtering

At this point everything has been configured properly, you can see one router is showing adjacency going up and down. Take a look if there is any access list blocking the IP traffic.

R1# show access-list

Definitely a guess method is not an option when you are trying to narrow down some issues and the clock is not from your side.

In my opinion an analysis through the layers L1, L2, L3 and EIGRP details should point you out the error.