Alcatel-lucent Scalable IP Networks OSPF

1. Which of the following is not a feature of the OSPF protocol?

It supports authentication.

It provides a loop-free topology.

It uses the Shortest Path First algorithm.

It uses a hop count-based metric.

OSPF uses a cost value on each interface that is based on the bandwidth of the link; it does not use a hop count.

Explanation

OSPF uses a cost value on each interface that is based on the bandwidth of the link; it does not use a hop count.

2. OSPF Discovers neighbors_______.

Only by manually configuring the router

By flooding updates

Using Hello advertisements

Using a host table

OSPF sends Hello packets to the 224.0.0.5 multicast IP address to discover other OSPF routers.

Explanation

OSPF sends Hello packets to the 224.0.0.5 multicast IP address to discover other OSPF routers.

3. Which statement best describes what happens when an OSPF receives an LSA with a higher sequence number than the LSA in its database?

The router acknowledges the LSA and floods it to its neighbors but does not add it to its link-state database.

The router acknowledges the LSA, adds it to its own database, and floods it to its neighbors.

A higher sequence number indicates that the received LSA has newer information than what the router currently has in its database. Therefore, the router will acknowledge the LSA, flood it to its neighbors, and add the LSA to its own database. Answer A describes the action when the sequence number is the same and B describes the action when the sequence number is lower (the LSA is out of date).

Explanation

A higher sequence number indicates that the received LSA has newer information than what the router currently has in its database. Therefore, the router will acknowledge the LSA, flood it to its neighbors, and add the LSA to its own database. Answer A describes the action when the sequence number is the same and B describes the action when the sequence number is lower (the LSA is out of date).

4. In addition to having correct OSPF settings in the Hello packets, another value that can prevent routers from forming an adjacency in the event of a mismatch is _____.

The AS number

The OSPF MTU

The OSPF metric

The MPLS TE

This is based on the interface MTU and must match on each router.

Explanation

This is based on the interface MTU and must match on each router.

5. What is the primary purpose of the OSPF router ID?

To elect a designated router

To uniquely identify an OSPF router

To trace sequence numbers

To support LSA flooding

Every OSPF router must have a router ID to uniquely identify it for purposes of building the SPF tree and identifying its LSA updates.

Explanation

Every OSPF router must have a router ID to uniquely identify it for purposes of building the SPF tree and identifying its LSA updates.

6. What is required for OSPF routers on a point-to-point network to form an adjacency?

The DR must form an adjacency first.

The neighbor IP address must be configured.

They will automatically become adjacent provided certain OSPF configuration values match.

Nothing. OSPF routers on point-to-point links will always become adjacent.

The area ID and Hello and dead timers must match in the Hello packets.

Explanation

The area ID and Hello and dead timers must match in the Hello packets.

7. There are many different types of LSAs in OSPF. The most common LSA type in point-to-point networks is _____.

The area LSA

The router LSA

The network LSA

The summary LSA

The router LSA carries the local topology information for each router in the network.

Explanation

The router LSA carries the local topology information for each router in the network.

8. LSA updates are sent in response to network changes and _____.

Every 30 minutes

After the Hello timer expires

When the DR detects the BDR has failed

Every 30 minutes provided new information needs to be transmitted

LSA updates are sent every 30 minutes in order to refresh the LSA. They are sent regardless of whether changes have occurred.

Explanation

LSA updates are sent every 30 minutes in order to refresh the LSA. They are sent regardless of whether changes have occurred.

9. What does it mean to say that two OSPF routers are adjacent?

The routers are physically connected on a point-to-point link.

The routers are on a common network segment and have exchanged database information.

The routers have exchanged Hello packets.

The routers are in a single area.

Routers that have shared database information are referred to as adjacent. Not all neighbor OSPF routers become adjacent.

Explanation

Routers that have shared database information are referred to as adjacent. Not all neighbor OSPF routers become adjacent.

10. Which of the following hello packet values is not involved in the adjacency process on point-to-point links?

The area ID

The priority

The Hello timer

The dead timer

The priority value is only applicable on OSPF broadcast networks.

Explanation

The priority value is only applicable on OSPF broadcast networks.

11. Which of the following correctly identifies the order of steps for two OSPF routers to become fully adjacent?

Exchange, Loading, SPF, Adjacent

Exchange, ExStart, Loading

ExStart, Exchange, Loading, Full

ExStart, Exchange, Loading, Adjacent

This is the correct order.

Explanation

This is the correct order.

12. Which logical interface is recommended for defining a router ID?

Ethernet interface

Chassis interface

MAC address

System interface

It is recommended that you use the system interface as the router ID.

Explanation

It is recommended that you use the system interface as the router ID.

13. If an OSPF router receives an LSA with a sequence number that is equal to the sequence number it already has for that LSA, it will _____.

Silently drop the LSA

Send a rejection notice to the sending router

Drop the LSA and send an acknowledgement

Drop the LSA and forward it to its adjacent routers

The router already has the information so it will drop the LSA, but all LSAs must be acknowledged.

Explanation

The router already has the information so it will drop the LSA, but all LSAs must be acknowledged.

14. Which of the following is false regarding the Shortest Path First algorithm that OSPF uses?

It determines the optimal route to each network.

It creates a loop-free path to each network.

It is run only on the router that originates an LSA update.

It runs every time a new LSA is received.

Whenever an LSA update is flooded throughout the network, all routers must rerun the SPF algorithm.

Explanation

Whenever an LSA update is flooded throughout the network, all routers must rerun the SPF algorithm.

15. Which of the following default metrics is not correct for the given interface speed?

1-Gbps link = 100

16-Mbps link = 6,250

1.544-Mbps link = 64,766

622-Mbps link = 16

(100 Gbps)/(622 Mbps) = 160, not 16.

Explanation

(100 Gbps)/(622 Mbps) = 160, not 16.

16. The command to display the Link State Updates that a router has received is _____.

Show router ospf status

Show router ospf links

Showrouter ospf summary

Show router ospf database

This command displays the LSAs that have been received from other OSPF routers.

Explanation

This command displays the LSAs that have been received from other OSPF routers.

17. What is the cost value of an OSPF interface on the Alcatel-Lucent 7750 SR?

It is based on the configuration of the global OSPF cost variable, which has a default value of 10.

It is based on the configuration of the global OSPF cost variable, which has a default value of 100.

It is based on a reference bandwidth, which has a default value of 10 Gbps.

It is based on a reference bandwidth, which has a default value of 100 Gbps.

The cost value in OSPF is dependent on the default OSPF reference bandwidth, which is 100Gbs.

Explanation

The cost value in OSPF is dependent on the default OSPF reference bandwidth, which is 100Gbs.

18. When does an OSPF router transition to the 2-Way state?

After a Link State Request is received from a neighbor

After the first Link State Update is received from a neighbor

After a Hello packet that contains its own router ID is received from a neighbor

After the first Link State Acknowledgment is received from a neighbor

After a Database Description packet is received from a neighbor

An OSPF router transitions to the 2-Way state after a Hello packet that contains its own router ID is received from a neighbor.

Explanation

An OSPF router transitions to the 2-Way state after a Hello packet that contains its own router ID is received from a neighbor.

19. What is the main purpose of the DBD packet?

The DBD packet is used to carry LSAs between routers.

The DBD packet is used in the OSPF neighbor discovery mechanism.

The DBD packet is used to provide summary LSA information to each router so that specific LSAs can be requested.

The DBD packet is used to withdraw LSA information when there is a topology change.

The DBD packet is used to provide summary LSA information to each router so that specific LSAs can be requested.

Explanation

The DBD packet is used to provide summary LSA information to each router so that specific LSAs can be requested.

20. R1 and R2 are directly connected to each other and running OSPF on the link. The OSPF interface MTU of both routers is different, but the port MTU of each router is the same. What state will the adjacency be in?

The adjacency will be in the Init state.

The adjacency will be in the 2-Way state.

The adjacency will be in the ExStart state.

The adjacency will be in the Full state.

By default, the OSPF MTU is derived from the port MTU. However, in this case, the OSPF MTU is explicitly set on the OSPF interface; thus there is definitely an MTU mismatch. Because the MTU is carried in the Database Description packet and the values do not match, the routers will stay in the ExStart state.

Explanation

By default, the OSPF MTU is derived from the port MTU. However, in this case, the OSPF MTU is explicitly set on the OSPF interface; thus there is definitely an MTU mismatch. Because the MTU is carried in the Database Description packet and the values do not match, the routers will stay in the ExStart state.

21. A router has been elected the DR on a broadcast OSPF interface on a subnet with three other routers. How will the link-state topology be described by routers on the subnet? Choose the best statement.

The DR originates only a Network LSA that describes the broadcast network.

Every OSPF router originates a Router LSA that describes all their interfaces regardless of the interface types. Therefore, answers A, B, and C are incorrect. Only the DR and BDR for a broadcast interface originate the Network LSA and, therefore, D is incorrect.

Explanation

Every OSPF router originates a Router LSA that describes all their interfaces regardless of the interface types. Therefore, answers A, B, and C are incorrect. Only the DR and BDR for a broadcast interface originate the Network LSA and, therefore, D is incorrect.

22. When two routers are in the OSPF ExStart state, how is the initial Database Description sequence number determined?

Both routers send a DBD packet with an initial sequence number, and the highest is used.

The sequence number of the router with the highest priority is used.

The sequence number of the router that sends the first Database Description packet is used.

The sequence number of the router with the highest router ID is used.

Both OSPF routers send an initial Database Description packet. The router with the highest router ID becomes the master, and the sequence number in its Database Description packet is used.

Explanation

Both OSPF routers send an initial Database Description packet. The router with the highest router ID becomes the master, and the sequence number in its Database Description packet is used.

23. A 7750 SR has an OSPF adjacency with its neighbor using a router ID derived from the last four octets of the chassis MAC address. The system interface IP address, router ID, and OSPF router ID are then configured. Assuming these are the only commands executed, what router ID will be seen by the OSPF neighbor?

The router ID seen by the neighbor will be derived from the last four octets of the chassis MAC address.

The router ID seen by the neighbor will be derived from the system interface address.

The router ID seen by the neighbor will be derived from the configured router ID.

The router ID seen by the neighbor will be derived from the configured OSPF router ID.

The router ID value does not change until the OSPF process is restarted. If OSPF is shut down and restarted, the router ID will be configured with the OSPF router ID value.

Explanation

The router ID value does not change until the OSPF process is restarted. If OSPF is shut down and restarted, the router ID will be configured with the OSPF router ID value.

24. Which of the following is not a field in an OSPF Hello packet that must match for a successful state transition to the 2-Way state?

Dead Interval

Authentication Type

MTU

Area ID

Stub Flag

The MTU must match, but the MTU value is not in the Hello packet; it is in the Database Description packet. If there is an MTU mismatch on the link, the routers will move past the OSPF 2-Way state. The other four parameters are all contained in the Hello packet and must match for the adjacency to continue.

Explanation

The MTU must match, but the MTU value is not in the Hello packet; it is in the Database Description packet. If there is an MTU mismatch on the link, the routers will move past the OSPF 2-Way state. The other four parameters are all contained in the Hello packet and must match for the adjacency to continue.

25. Which of the following best describes the election of the DR on a broadcast interface in OSPF when all routers have the same priority value?

The router with the lowest router ID is always the DR.

The router with the highest router ID is always the DR.

The router with the highest IP address on the broadcast interface is always the DR.

The router with the lowest IP address on the broadcast interface is always the DR.

The router that has been up the longest is usually the DR, since DR election is non-preemptive.

If the priority of the routers is the same and there is no DR already elected, the router with the highest router ID on the network is elected DR. However, DR election is non-preemptive. If a router is already DR, it remains DR even when a router with a higher priority joins the network. Thus, the DR is often the router on the network that has been up the longest.

Explanation

If the priority of the routers is the same and there is no DR already elected, the router with the highest router ID on the network is elected DR. However, DR election is non-preemptive. If a router is already DR, it remains DR even when a router with a higher priority joins the network. Thus, the DR is often the router on the network that has been up the longest.

26. A router has an OSPF broadcast interface declared as passive. How will this be represented in the Router LSA originated by the router?

The Router LSA will contain a stub network link type to describe the interface.

The Router LSA will contain a transit link type to describe the interface.

The Router LSA will contain a point-to-point link type to describe the interface.

The Router LSA will contain a point-to-point link type and a stub network link type to describe the interface.

The Router LSA will not describe the interface.

All passive interfaces, loopback interfaces, system interfaces, and interfaces that have not yet formed an adjacency are represented in the Router LSA as stub networks.

Explanation

All passive interfaces, loopback interfaces, system interfaces, and interfaces that have not yet formed an adjacency are represented in the Router LSA as stub networks.

27. Which statement is not correct regarding an OSPF Type 1 LSA?

An OSPF Type 1 LSA is originated by every OSPF router.

An OSPF Type 1 LSA is called a Router LSA.

The OSPF Type 1 LSA is flooded throughout the autonomous system.

The OSPF Type 1 LSA describes the router’s directly connected links.

The OSPF Type 1 LSA contains an age field.

The OSPF Router LSA (Type 1 LSA) is not flooded throughout the autonomous system; it is only flooded within the area in which it was originated.

Explanation

The OSPF Router LSA (Type 1 LSA) is not flooded throughout the autonomous system; it is only flooded within the area in which it was originated.

28. Which statement is correct regarding OSPF LSA exchange between routers?

A router requests one LSA at a time using an LSR.

A router never requests LSAs; they are always flooded.

A router can request multiple LSAs using a single LSR. The size of the LSR is limited by the OSPF interface MTU setting.

Explanation

A router can request multiple LSAs using a single LSR. The size of the LSR is limited by the OSPF interface MTU setting.

29. Two routers R1 and R2 have a point-to-point OSPF adjacency. R1 has a priority of 15 and an OSPF router ID of 10.10.10.10. R2 has a priority of 25 and an OSPF router ID of 5.5.5.5. Which router will be the Designated Router?

R1 will be the Designated Router.

R2 will be the Designated Router.

The first router to initialize will be the Designated Router.

There will be no Designated Router.

OSPF routers on a point-to-point link do not elect a designated router, only routers on a broadcast link.

Explanation

OSPF routers on a point-to-point link do not elect a designated router, only routers on a broadcast link.

30. A router has four interfaces that are added to OSPF. Two point-to-point interfaces are in Area 1. There is one point-to-point interface in Area 2 and one broadcast interface in Area 3. How many Network LSAs will be originated by the router?

The router will not originate any Network LSAs.

The router will originate one Network LSAs.

The router will originate two Network LSAs.

The router will originate four Network LSAs.

It is not possible to determine with the given information.

Network LSAs are originated by the elected DR for an OSPF broadcast network, and we do not know if the router is the DR or not. If the router is the DR for the broadcast network in area 3, the router originates one Network LSA. If the router is not the DR for the broadcast network in area 3, it does not originate any Network LSAs. Network LSAs are not originated for any of the point-to-point networks.

Explanation

Network LSAs are originated by the elected DR for an OSPF broadcast network, and we do not know if the router is the DR or not. If the router is the DR for the broadcast network in area 3, the router originates one Network LSA. If the router is not the DR for the broadcast network in area 3, it does not originate any Network LSAs. Network LSAs are not originated for any of the point-to-point networks.