New CCNA – OSPF Questions 2

Note: If you are not sure about OSPF, please read our OSPF Tutorial.

Question 1

Why R1 can’t establish an OSPF neighbor relationship with R3 according to the following graphic? (Choose two)

A – Configure EIGRP on these routers with a lower administrative distance
B – All routers should be configured for backbone Area 1
C – R1 and R3 have been configured in different areas
D – The hello and dead interval timers are not configured the same values on R1 and R3

 

Answer: C D

Explanation

A is not correct because configure EIGRP on these routers (with a lower administrative distance) will force these routers to run EIGRP, not OSPF.

B is not correct because the backbone area of OSPF is always Area 0.

C and D are correct because these entries must match on neighboring routers:

- Hello and dead intervals
– Area ID (Area 0 in this case)
– Authentication password
– Stub area flag

Question 2

Which parameter or parameters are used to calculate OSPF cost in Cisco routers?

A. Bandwidth, Delay and MTU
B. Bandwidth
C. Bandwidth and MTU
D. Bandwidth, MTU, Reliability, Delay and Load

 

Answer: B

Explanation

The well-known formula to calculate OSPF cost is

Cost = 10⁸ / Bandwidth

so B is the correct answer.

Question 3

A network administrator is troubleshooting the OSPF configuration of routers R1 and R2. The routers cannot establish an adjacency relationship on their common Ethernet link. The graphic shows the output of the show ip ospf interface e0 command for routers R1 and R2. Based on the information in the graphic, what is the cause of this problem?

A. The OSPF area is not configured properly.
B. The priority on R1 should be set higher.
C. The cost on R1 should be set higher.
D. The hello and dead timers are not configured properly.
E. A backup designated router needs to be added to the network.
F. The OSPF process ID numbers must match.

 

Answer: D

Explanation

D is correct because these entries must match on neighboring routers:

- Hello and dead intervals
– Area ID (Area 0 in this case)
– Authentication password
– Stub area flag

In this case Ethernet0 of R1 has Hello and Dead Intervals of 5 and 20 while R2 has Hello and Dead Intervals of 10 and 40 -> R1 and R2 cannot form OSPF neighbor relationship.

Question 4

What information does a router running a link-state protocol use to build and maintain its topological database? (Choose two)

A. hello packets
B. SAP messages sent by other routers
C. LSAs from other routers
D. beacons received on point-to-point links
E. routing tables received from other link-state routers
F. TTL packets from designated routers

 

Answer: A C

Question 5

Which command is used to display the collection of OSPF link states?
A. show ip ospf link-state
B. show ip ospf lsa database
C. show ip ospf neighbors
D. show ip ospf database

 

Answer: D

Question 6

When running OSPF, what would cause router A not to form an adjacency with router B?

A. The loopback addresses are on different subnets.
B. The values of the dead timers on the routers are different.
C. Route summarization is enabled on both routers.
D. The process identifier on router A is different than the process identifier on router

Answer: B

Explanation

To form an adjacency (become neighbor), router A & B must have the same Hello interval, Dead interval and AREA number.

Question 7

Which is true about OSPF router-id? (Choose two)

A. It is used for type 1 router LSA
B. Highest IP address of the loopback is used
C. router-id needs to be matched on ospf neighbors
D. router-id is 16 bit

 

Answer: A B

Explanation

OSPF LSA Type 1 (or Router LSA) is generated by all routers in an area to describe their directly attached links. An example below shows this type of LSA:

As you can see, the LSA Type 1 uses the router ID to advertise itself (1.1.1.1 or 2.2.2.2).

The Router ID (RID) is an IP address used to identify the router and is chosen using the following sequence:
+ The highest IP address assigned to a loopback (logical) interface.
+ If a loopback interface is not defined, the highest IP address of all active router’s physical interfaces will be chosen.
+ The router ID can be manually assigned

Question 8

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

A. It identifies the source of 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: A D

Explanation

From the output of the “show ip ospf database”:

We can see OSPF Router ID will be used as source of Type 1 LSA (1.1.1.1 & 2.2.2.2). Also the router will chose the highest loopback interface as its OSPF router ID (if available).

Question 9

What are two benefits of using a single OSPF area network design? (Choose two)

A. It is less CPU intensive for routers in the single area.
B. It reduces the types of LSAs that are generated.
C. It removes the need for virtual links.
D. It increases LSA response times.
E. It reduces the number of required OSPF neighbor adjacencies.

 

Answer: B C