Scenario
Refer to the topology. Your company has decided to connect the main office with three other remote branch offices using point-to-point serial links.
You are required to troubleshoot and resolve OSPF neighbor adjacency issues between the main office and the routers located in the remote branch offices.
Use appropriate show commands to troubleshoot the issues and answer all four questions.
Instructions
An OSPF neighbor adjacency is not formed between R3 in the main office and R6 in the Branch3 office. What is causing the problem?
A.
There is an area ID mismatch.
B.
There is a PPP authentication issue; the username is not configured on R3 and R6.
C.
There is an OSPF hello and dead interval mismatch.
D.
The R3 router ID is configured on R6.
Explanation:
Here are the relevant parts of the router configs:
R1interface Loopback0description ***Loopback***ip address 192.168.1.1 255.255.255.255ip ospf 1 area 0!interface Ethernet0/0description **Connected to R1-
LAN**ip address 10.10.110.1 255.255.255.0ip ospf 1 area 0!interface Ethernet0/1description **Connected to L2SW**ip address 10.10.230.1 255.255.255.0ip ospf
hello-interval 25ip ospf 1 area 0!router ospf 1log-adjacency-changes
R2!interface Loopback0description **Loopback**ip address 192.168.2.2 255.255.255.255ip ospf 2 area 0!interface Ethernet0/0description **Connected to R2-
LAN**ip address 10.10.120.1 255.255.255.0ip ospf 2 area 0!interface Ethernet0/1description **Connected to L2SW**ip address 10.10.230.2 255.255.255.0ip ospf 2
area 0!router ospf 2log-adjacency-changes
R3username R6 password CISCO36!interface Loopback0description **Loopback**ip address 192.168.3.3 255.255.255.255ip ospf 3 area 0!interface
Ethernet0/0description **Connected to L2SW**ip address 10.10.230.3 255.255.255.0ip ospf 3 area 0!interface Serial1/0description **Connected to R4-Branch1
office**ip address 10.10.240.1 255.255.255.252encapsulation pppip ospf 3 area 0!interface Serial1/1description **Connected to R5-Branch2 office**ip address
10.10.240.5 255.255.255.252encapsulation pppip ospf hello-interval 50ip ospf 3 area 0!interface Serial1/2description **Connected to R6-Branch3 office**ip address
10.10.240.9 255.255.255.252encapsulation pppip ospf 3 area 0ppp authentication chap!router ospf 3router-id 192.168.3.3!
R4!interface Loopback0description **Loopback**ip address 192.168.4.4 255.255.255.255ip ospf 4 area 2!interface Ethernet0/0ip address 172.16.113.1
255.255.255.0ip ospf 4 area 2!interface Serial1/0description **Connected to R3-Main Branch office**ip address 10.10.240.2 255.255.255.252encapsulation pppip
ospf 4 area 2!router ospf 4log-adjacency-changes
R5!interface Loopback0description **Loopback**ip address 192.168.5.5 255.255.255.255ip ospf 5 area 0!interface Ethernet0/0ip address 172.16.114.1
255.255.255.0ip ospf 5 area 0!interface Serial1/0description **Connected to R3-Main Branch office**ip address 10.10.240.6 255.255.255.252encapsulation pppip
ospf 5 area 0!router ospf 5log-adjacency-changes
R6username R3 password CISCO36!interface Loopback0description **Loopback**ip address 192.168.6.6 255.255.255.255ip ospf 6 area 0!interface Ethernet0/0ip
address 172.16.115.1 255.255.255.0ip ospf 6 area 0!interface Serial1/0description **Connected to R3-Main Branch office**ip address 10.10.240.10
255.255.255.252encapsulation pppip ospf 6 area 0ppp authentication chap!router ospf 6router-id 192.168.3.3!
R3#show running-config<<output omitted>>username R6 password CISCO36!interface Serial1/2description **Connected to R6-Branch3 office**ip address
10.10.240.9 255.255.255.252encapsulation pppip ospf 3 area 0ppp authentication chap!<<output omitted>>!router ospf 3router-id 192.168.3.3!<<output omitted>>
R6#show running-config<<output omitted>>username R3 password CISCO36!interface Serial1/0description **Connected to R3-Main Branch office**ip address
10.10.240.10 255.255.255.252encapsulation pppip ospf 6 area 0ppp authentication chap!<<output omitted>>!router ospf 6router-id 192.168.3.3!<<output
omitted>>
We are not sure about the configuration of ppp authentication in this case. Some reports said that only one router has the “ppp authentication chap” command but it
is just a trick and is not the problem here. The real problem here is R6 uses the same router-id of R3 (192.168.3.3) so OSPF neighborship cannot be established.
In real life, such configuration error will be shown in the command line interface (CLI). So please check carefully for this question.