Cisco 200-105 Exam

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.
Answer: Option A. D.
Explanation: 

From the output of the “show ip ospf
database”: r120#show ip ospf data
OSPF Router with ID (10.0.0.120) (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
10.0.0.111 10.0.0.111 600 0x8000023A 0x0092B3 1
10.0.0.112 10.0.0.112 1246 0x80000234 0x009CAC 1
10.0.0.113 10.0.0.113 148 0x8000022C 0x004399 3
10.0.0.120 10.0.0.120 152 0x80000240 0x0046CB 1
This tells us there are four routers in Area 1. The router with RID 10.0.0.113 has 3 links in Area 1, everyone else has only 1 link. Also the router will choose the highest loopback interface as its OSPF router ID (if available).

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