OSPF Concepts

Question 1

What are the 5 OSPF exchange messages? What are they used to accomplish?

Answer 1

1. Hello packet
2. Database description packet
3. Link-state request packet
4. link-state update packet
5. link state acknowledgment

Used to discover neighboring routers and exchange/maintain info about the network.

Question 2

Which of the following OSPF components is associated with the neighbor table?

Answer 2

adjacency database

Question 3

Which of the following OSPF components is responsible for computing the cost of each route?

Answer 3

Dijkstra’s algorithm

Question 3

Which of the following OSPF components is associated with the topology table?

Answer 3

link-state database

Question 4

Which of the following OSPF components is associated with the routing table?

Answer 4

Forwarding database

Question 5

What is the correct order in the steps for Link-State operation?

Answer 5

1. establish neighbor adjacencies
2. exchange link-state advertisements
3. build the topology table
4. execute the SPF algorithm
5. choose the best route

Question 6

What are hello packets used for?

Answer 6

Hello packet - This is used to establish and maintain adjacency with other OSPF routers.

Question 7

What are Database Description (DBD) packets used for?

Answer 7

Database Description (DBD) packet - This contains an abbreviated list of the LSDB of the sending router and is used by receiving routers to check against the local LSDB. The LSDB must be identical on all link-state routers within an area

Question 8

what are Link-State Request (LSR) packets used for?

Answer 8

Receiving routers can then request more information about any entry in the DBD by sending an LSR.

Question 9

What are Link-State Update (LSU) packets used for?

Answer 9

Link-State Update (LSU) packet - This is used to reply to LSRs and to announce new information. LSUs contain several different types of LSAs.

Question 10

What are Link-State Acknowledgment (LSAck) packets used for?

Answer 10

Link-State Acknowledgment (LSAck) packet - When an LSU is received, the router sends an LSAck to confirm receipt of the LSU. The LSAck data field is empty.

Question 11

Which of the following OSPF packets contains an abbreviated list of the LSDB of the sending router?

Answer 11

DBD packet (Database Description)

Question 12

Which of the following OSPF packets is used by routers to announce new information?

Answer 12

LSU packet (link-state update)

Question 13

Which of the following OSPF packets is used by routers to request more information?

Answer 13

LSR packet (link-state request)

Question 14

Which of the following OSPF packets is responsible for establishing and maintaining adjacency with other OSPF routers?

Answer 14

Hello packet

Question 15

Which of the following OSPF packets is used to confirm receipt of an LSA?

Answer 15

LSAck packet

Question 16

Which of the following is used with the Hello Packet to uniquely identify the originating router?

Answer 16

Router ID

Question 17

Is an Ethernet network multiaccess or a single-access network?

Answer 17

Ethernet is a multiple-access network. This means that multiple nodes can send and receive data over a shared link.

Question 18

How often are Hello packets sent out? How long until dead interval?

Answer 18

On Ethernet interfaces you will see a 10-second hello interval and a 40-second dead interval.