Exam 200-125 topic 1 question 15 discussion

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 R5 in the Branch2 office. What is causing the problem?

Suggested Answer: Explanation 🗳️
Here are the relevant parts of the router configs:

Continue checking their connected interfaces with the "show running-config" command:


The only difference we can see here is the line "ip ospf hello-interval 50″ on R3. This command sets the number of seconds R3 waits before sending the next hello packet out this interface. In this case after configuring this command, R3 will send hello packets to R5 every 50 seconds. But the default value of hello-interval is
10 seconds and R5 is using it. Therefore we can think of a hello interval mismatch problem here. You can verify with the "show ip ospf interface <interface>" command on each router.

So we can see both hello and dead interval are mismatched because the dead interval always four times the value of hello interval, unless you manually configure the dead interval (with the ip ospf dead-interval <seconds> command).