JNCIS-SP: Juniper Networks Certified Specialist – Service Provider Routing — Question 46

You are configuring OSPF on a Junos device; however, you have not configured a router ID.
What is the default behavior in this situation?

Answer options

• A. If the loopback is configured with a 127/8 address, it will be used.
• B. If the loopback is not configured, it will use the interface with the highest IP address.
• C. If the loopback is configured and does not have a usable address, the IP address associated with the first hardware interface is used.
• D. If you configure a dedicated management address and include that interface in OSPF, it will be used as the router ID.

Correct answer: C

Explanation

The correct answer is C because if the loopback interface is not assigned a usable address, OSPF defaults to the IP address of the first hardware interface. Option A is incorrect because it deals with the loopback's address status, which doesn't apply if it is not usable. Option B is wrong since it only mentions the highest IP address scenario, disregarding the loopback's role. Option D is also incorrect, as the dedicated management address does not take precedence if the loopback is available but unusable.