CCNA Exam Preparations

Which of the following factors determines the OSPF router ID when configuring a router with both
physical and logical interfaces?

A. The lowest network number of any interface.
B. The highest network number of any interface.
C. The highest IP address of any logical interface.
D. The middle IP address of any logical interface.
E. The lowest IP address of any physical interface.
F. The highest IP address of any physical interface.
G. The lowest IP address of any logical interface.

Answer :
Answer: F
Explanation:
The OSPF topology database includes information about routers and the subnets, or links, to which they are
attached. To identify the routers in the neighbor table’s topology database, OSPF uses a router ID (RID) for
each router. A router’s OSPF RID is that router’s highest IP address on a physical interface when OSPF starts
running.

Note: The OSPF router ID is a 32-bit IP address selected at the beginning of the OSPF process. The highest IP
address configured on the router is the router ID. If a loopback address is configured, then it is the router ID. In
case of multiple loopback addresses, the highest loopback address is the router ID. Once the router ID is elected
it doesn't change unless the IP address is removed or OSPF restarts.