What is the sequence, from first to last, that OSPF will follow when choosing a router ID?
A.
1. the highest IP address on any active loopback interface; 2. The router-id command results; 3.
The highest IP address of any active physical interface.
B.
1. the highest IP address on any active loopback interface; 2. The highest IP address of any
active Physical interface; 3. The router-id command result.
C.
1. The highest IP address of any active Physical interface; 2. the highest IP address on any
active loopback interface; 3. The router-id command results.
D.
1. The highest IP address of any active Physical interface; 2. The router-id command result; 3.
The highest IP address of any active physical interface.
E.
1. The router-id command results; 2. The highest IP address of any active Physical interface; 3.
The highest IP address of any active physical interface.
F.
1. the router-id command result; 2. the highest IP address on any active loopback interface; 3.
the highest IP address of any active physical interface
Explanation:
1. The router chooses the numerically highest IP address on any of its loopback interfaces.
2. If no loopback interfaces are configured with IP addresses, the router chooses the numerically
highest IP address on any of its physical interfaces. The interface from which the Router ID is
taken does not have to be running OSPF.
Using addresses associated with loopback interfaces has two advantages:
The loopback interface is more stable than any physical interface. It is active when the router
boots up, and it only fails if the entire router fails.
The network administrator has more leeway in assigning predictable or recognizable addresses as
the Router IDs.
Cisco’s OSPF will continue to use a Router ID learned from a physical interface even if the
interface subsequently fails or is deleted. Therefore, the stability of a loopback interface is only a
minor advantage. The primary benefit is the ability to control the Router ID.
The OSPF router begins a neighbor relationship by advertising its Router ID in Hello packets.