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Cisco CCNA 640-802 and 200-120 Exam Case Study:

Frame Relay Map Statements And Routing Protocols

By Chris Bryant, CCIE #12933

Your Cisco CCNA certification training includes learning how to troubleshoot, and nothing beats troubleshooting your own Cisco router lab configurations.

That’s when you see your CCNA theory taking place on Cisco routers, and that’s when you do your best learning. One recent experience a student and CCNA certification candidate ran into recently involved two major CCNA exam topics – Frame Relay map statements and their behavior with routing protocols such as RIP.

This student was running a CCNA lab and configured Frame Relay map statements with R1 serving as the hub router and R2 and R3 as spokes. After entering the following configuration on R1 and similar commands on R2 and R3, the configuration was tested with pings. Each router was able to ping the other two.

frame-relay map ip 172.12.123.2 122
frame-relay map ip 172.12.123.3 123

The CCNA certification candidate then configured RIP version 2 on the routers, and noticed that no routes were being exchanged between the three routers. The key to troubleshooting Cisco routers (and passing the CCNA exam) is knowing and using debugs, so the candidate ran debug ip rip followed by clear ip route * to quickly get some feedback from the router. This is what that feedback looked like, in part:

03:33:01: IP: s=172.12.123.1 (local), d=224.0.0.9 (Serial0), len 72, sending broad/multicast

03:33:01: IP: s=172.12.123.1 (local), d=224.0.0.9 (Serial0), len 72, encapsulation failed

When you have a routing problem, it’s human nature to look at the routing protocol configuration. You can’t look at Layer Three exclusively, though, because the problem just might be an a lower layer in the OSI model. In this case, the reason the RIP update packets were not being sent was because of a problem at Layer Two – the Frame Relay configuration!

Cisco CCNA Certification - It's All About Noticing Details

You might be wondering what kind of problem we could have with Frame Relay if the pings are going through. The pings aren’t broadcasts or multicasts, but RIP updates are one or the other. RIP version 1 updates are broadcasts, and RIP version 2 updates are multicast to 224.0.0.9. For either to go through, the “broadcast” option must be enabled on the Frame Relay map statements!

The candidate reconfigured the frame map statements on R1, R2, and R3 to include the broadcast option. The R1 reconfiguration is shown below:

R1(config-if)#frame map ip 172.12.123.2 122 broadcast

R1(config-if)#frame map ip 172.12.123.3 123 broadcast

As a result, the RIP updates began to be sent and received successfully. The following is the output of debug ip rip once the frame map statements were reconfigured.

06:22:13: RIP: sending general request on Loopback0 to 224.0.0.9

06:22:13: RIP: sending general request on Serial0 to 224.0.0.9

06:22:14: RIP: received v2 update from 172.12.123.3 on Serial0

06:22:14: 1.1.1.1/32 -> 0.0.0.0 in 3 hops

06:22:14: 2.2.2.2/32 -> 0.0.0.0 in 2 hops

06:22:14: 3.3.3.3/32 -> 0.0.0.0 in 1 hops

06:22:14: RIP: sending v2 update to 224.0.0.9 via Serial0 (172.12.123.1)

06:22:14: 2.2.2.2/32 -> 0.0.0.0, metric 3, tag 0

06:22:14: 3.3.3.3/32 -> 0.0.0.0, metric 2, tag 0

Your exam success depends on being able to spot issues like this, and so does your success in real-world networks. Nothing beats practicing on Cisco routers and switches – nothing!

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