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Frame Relay, Pings, And Routing


Cisco CCNA certification training includes troubleshooting your own work and that of others. The best CCNA training you can do is indeed troubleshooting your own Cisco router and switch configurations - as I'm always telling my students, "I can guarantee that any error you make has been made before, and you'll probably see it again one day." One such common error involves two very important Cisco CCNA certification topics - Frame Relay and routing protocols.

A student was working on his Cisco CCNA exam home lab and came up with an interesting problem. He set Frame Relay up in a hub-and-spoke configuration with R1 as the hub and R2 and R3 as the spokes. He wrote the following frame map statements:

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


He was able to ping both spokes from the hub, so he assumed everything was working correctly. Then he configured RIP version 2 on the router and got the following result after running "debug ip rip" and clearing the routing table with "clear ip route *":

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


You may have already spotted the problem, and if you did, your CCNA certification exam studies are going well! The problem is that the "broadcast" option was left off the frame map statements. "broadcast" must be configured on frame map statements in order to send broadcasts and multicasts across the frame link. As you know from your CCNA certification exam studies, RIP version 1 broadcasts updates and RIP version 2 multicasts them, so the "broadcast" option must be present for either version to send updates by using those frame mappings.

He then rewrote the frame map statements as 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


... and the RIP updates went out as expected.

R1#debug ip rip
RIP protocol debugging is on
R1#clear ip route *
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
06:22:13: RIP: ignored v2 packet from 1.1.1.1 (sourced from one of our addresses )
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: 172.12.23.0/24 -> 0.0.0.0 in 1 hops
06:22:14: 172.12.123.0/24 -> 0.0.0.0 in 1 hops
06:22:14: RIP: sending v2 update to 224.0.0.9 via Loopback0 (1.1.1.1)
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
06:22:14: 172.12.23.0/24 -> 0.0.0.0, metric 2, tag 0
06:22:14: 172.12.123.0/24 -> 0.0.0.0, metric 1, tag 0
06:22:14: RIP: sending v2 update to 224.0.0.9 via Serial0 (172.12.123.1)


Cisco CCNA certification depends on noticing details like these, and there's no better way to learn these details than by working on real Cisco routers and switches. Whether you're renting rack time online or buying used Cisco routers and switches, real-time debugs and configurations are the way to CCNA certification exam success!

About the Author:
Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage , home of free CCNA and CCNP tutorials! Pass the CCNA exam with Chris Bryant!





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