CISCO CCNA Exam – Q159

Which two statements about the OSPF Router ID are true? (Choose two.)

A. It identifies the source of a Type 1 LSA.
B. It should be the same on all routers in an OSPF routing instance.
C. By default, the lowest IP address on the router becomes the OSPF Router ID.
D. The router automatically chooses the IP address of a loopback as the OSPF Router ID.
E. It is created using the MAC Address of the loopback interface.

Correct Answers: A, D

r120#show ip ospf data
OSPF Router with ID ( (Process ID 1)
Next, who are the other routers in our area?
Router Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Link count 600 0x8000023A 0x0092B3 1 1246 0x80000234 0x009CAC 1 148 0x8000022C 0x004399 3 152 0x80000240 0x0046CB 1

We can see OSPF Router ID will be used as source of Type 1 LSA. Also the router will chose the highest loopback interface as its OSPF router ID (if available).