Test Your Knowledge Is On CCNA – OSPF Questions 2

1. 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?

The OSPF area is not configured properly.

The priority on R1 should be set higher.

The cost on R1 should be set higher.

The hello and dead timers are not configured properly.

A backup designated router needs to be added to the network.

The OSPF process ID numbers must match.

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.

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.

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

Bandwidth, Delay and MTU

Bandwidth

Bandwidth and MTU

Bandwidth, MTU, Reliability, Delay and Load

The well-known formula to calculate OSPF cost is

Cost = 108 / Bandwidth

so B is the correct answer.

Explanation

The well-known formula to calculate OSPF cost is

Cost = 108 / Bandwidth

so B is the correct answer.

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

The loopback addresses are on different subnets.

The values of the dead timers on the routers are different.

Route summarization is enabled on both routers.

The process identifier on router A is different than the process identifier on router

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

Explanation

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

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

It identifies the source of Type 1 LSA

It should be the same on all routers in an OSPF routing instance

By default, the lowest IP address on the router becomes the OSPF router ID

The router automatically chooses the IP address of a loopback as the OSPF Router ID

It is created using the MAC Address of the loopback interface

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

Explanation

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

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

Hello packets

SAP messages sent by other routers

LSAs from other routers

Beacons received on point-to-point links

Routing tables received from other link-state routers

TTL packets from designated routers

A router running a link-state protocol uses hello packets to establish and maintain neighbor relationships with other routers. These hello packets allow routers to exchange information about their presence and capabilities. Additionally, the router uses LSAs (Link State Advertisements) from other routers to build and maintain its topological database. LSAs contain information about the router's directly connected links and their state, which helps the router to construct a map of the network topology.

Explanation

A router running a link-state protocol uses hello packets to establish and maintain neighbor relationships with other routers. These hello packets allow routers to exchange information about their presence and capabilities. Additionally, the router uses LSAs (Link State Advertisements) from other routers to build and maintain its topological database. LSAs contain information about the router's directly connected links and their state, which helps the router to construct a map of the network topology.

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

It is used for type 1 router LSA

Highest IP address of the loopback is used

Router-id needs to be matched on ospf neighbors

Router-id is 16 bit

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:

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:

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

Configure EIGRP on these routers with a lower administrative distance

All routers should be configured for backbone Area 1

R1 and R3 have been configured in different areas

The hello and dead interval timers are not configured the same values on R1 and R3

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

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

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8. Which command is used to display the collection of OSPF link states?

Show ip ospf link-state

Show ip ospf lsa database

Show ip ospf neighbors

Show ip ospf database

The correct answer is "show ip ospf database". This command is used to display the collection of OSPF link states. It provides information about the OSPF database, which includes information about the OSPF routers, networks, and link states in the OSPF domain. By using this command, network administrators can view the OSPF link state database and gather information about the OSPF network topology.

Explanation

The correct answer is "show ip ospf database". This command is used to display the collection of OSPF link states. It provides information about the OSPF database, which includes information about the OSPF routers, networks, and link states in the OSPF domain. By using this command, network administrators can view the OSPF link state database and gather information about the OSPF network topology.

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

It is less CPU intensive for routers in the single area.

It reduces the types of LSAs that are generated.

It removes the need for virtual links.

It increases LSA response times.

It reduces the number of required OSPF neighbor adjacencies.

A single OSPF area network design reduces the types of Link State Advertisements (LSAs) that are generated. In a single area, only one type of LSA, known as Type 1 LSA, is generated. This simplifies the network design and reduces the complexity of OSPF routing. Additionally, a single area design removes the need for virtual links. Virtual links are used to connect non-backbone areas through the backbone area. By using a single area design, the need for virtual links is eliminated, which further simplifies the network and reduces potential configuration errors.

Explanation

A single OSPF area network design reduces the types of Link State Advertisements (LSAs) that are generated. In a single area, only one type of LSA, known as Type 1 LSA, is generated. This simplifies the network design and reduces the complexity of OSPF routing. Additionally, a single area design removes the need for virtual links. Virtual links are used to connect non-backbone areas through the backbone area. By using a single area design, the need for virtual links is eliminated, which further simplifies the network and reduces potential configuration errors.

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