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You are in the CCIE Routing and Switching Lab Exam and you have just begun the fun with the two hour Troubleshooting section. While speed reading the various Trouble Tickets, you notice that one seems rather simple. A router should be receiving routes from another router and it is not. From the diagram, you can quickly see that it is EIGRP that should be providing the route information.
First, confirmation that the routes are truly not in the routing table. This is accomplished quickly and efficiently with:
show ip route eigrp
Could it be that we are not learning the routes because an adjacency has failed? I guess the title of this blog post provides us the answer pretty quickly, but in the lab exam, we can quickly confirm this with:
show ip eigrp neighbor
What could cause such a neighborship to fail? I think it would be wise to commit a list of possible reasons to memory, and do this BEFORE starting the hectic paced Troubleshooting section. We do this after our in-depth studies of EIGRP itself in our study plan.
Here are possible reasons the EIGRP adjacency can fail:
- AS mismatch
- Lack of multicast support on the media
- Passive-interface
- Unicast neighbor misconfigured
- Authentication misconfiguration
- Security filtering
- Unidirectional Link
- Other Layer 2 link problem
- Administratively shutdown
- Primary and secondary address mismatch
- Misconfigured subnet mask
- K value mismatch
- Stuck in Active
- Misconfigured network command
I am sure that you can think of others that you have seen in the lab or in production environments and I encourage you to share your thoughts in the comments area below.
As you prepare for the Troubleshooting section of the lab, make a list like that of the above and then spend some time thinking about how you would most quickly determine if the potential issue is indeed the lab problem. You should even consider configuring two routers and attempting to set up the problem in each case to observe how the symptom could be quickly discovered.
When you are initially troubleshooting, try and pick very powerful commands that allow you to verify as much information as possible in one command. For example, show ip protocols, allows you to verify the following points in just one set of command output. To quickly determine several of our points here that relate purely to adjacency issues, we can quickly see :
- The AS the local device is configured for
- The K values
- The networks we are configured to route for
Always remember that a powerful trick that Cisco can use against you is to configure multiple problems that will cause the adjacency to fail. This will certainly help separate the true CCIE candidates from the more faint of heart. Be ready to continue your exploration quickly and efficiently if you have discovered and fixed an issue, yet the adjacency remains no where to be seen. You might even consider working in a bottom up approach once you realize there are several things wrong.
Happy hunting everyone!
Anthony Sequeira CCIE, CCSI
Twitter: @compsolv
Facebook: http://www.facebook.com/compsolv
Tags: CCIE, CCIE R&S, CCIE Routing and Switching, CCIE Training
