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MPLS TDP Neighbor Lab Sim

Question

R1 and R2 are not able to establish MPLS TDP neighbor relationship between them. Use various show commands to troubleshoot the problem then use the proper configuration command(s) to solve the MPLS TDP issue. Once R1 and R2 can see each other as MPLS TDP neighbor, then you have successfully completed the simulation.

Privileged mode password: mpls

MPLS_TDP.jpg

 

Answer and Explanation

Before reading the answer and explanation, you can try solving this question yourself by download the initial configuration and running it with GNS 3 here:

Download MPLS Lab Sim Initial Configuration GNS3 file

(Notice that the only difference of this file and the real exam is it doesn’t have privileged mode password and the interfaces between 2 routers are S1/0, not S0/0 and S0/1. The IOS used is c3660-jk9o3s-mz.124-17.bin. Also, you must change the image and config paths of the net file to make it work well )

Use the “show mpls ldp neighbor” or “show tag-switching tdp neighbor” command on both routers to see their neighbor relationship.

R1 (and R2)# show mpls ldp neighbor

We notice that the outputs show nothing, meaning that the TDP neighbor between two routers has not been established.

(Note: We can use the “show mpls ldp neighbor” to view the TDP neighbors because this command displays the state of both TDP and LDP neighbors. If not, you can use the “show tag-switching tdp neighbor” command instead)

Now use the show running-config command on both routers and notice in the RIP section

R1 (and R2)#show running-config

MPLS_TDP_show_run.jpg

The problem here is when a loopback interface is configured on the router, it will automatically become the TDP-id of that router (same as the router-id) but we didn’t declare this network in the RIP configuration -> MPLS TDP neighbor failed.

You can also check to see which interface is used as the TDP-id by the “show mpls ldp discovery” (notice the command is ldp, not tdp)

R1# show mpls ldp discovery

MPLS_TDP_show_mpls_ldp_discovery.jpg

To fix this, we have to declare the router’s loopback network in the RIP configuration

R1#configure terminal
R1(config)#router rip
R1(config-router)#network 1.0.0.0
R1(config-router)#end

R2#configure terminal
R2(config)#router rip
R2(config-router)#network 2.0.0.0
R2(config-router)#end

Now if we use the “show mpls ldp neighbor” again we can see the neighbor relationship has been established.

R1# show mpls ldp neighbor

MPLS_TDP_show_mpls_ldp_discovery_after.jpg

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