Online Quiz — Test 1

Correct Answer: B. B. Adds it to the database
Explanation: An OSPF router receives an LSA. If the router checks its sequence number and finds that the number is higher than the sequence number of the LSA that it already has, the router adds it to the database, and then floods the LSA to the other routers.

Correct Answer: C. C. Sends newer lsu update to source router
Explanation: An OSPF router receives an LSA. If the router checks its sequence number and finds that this number is lower than the sequence number that it already has, the router sends newer LSU update to source router. The router then adds it to the database and floods it to the other routers.

Correct Answer: C. C. 30 minutes
Explanation: Each LSA has its own age timer. By default, an LSA waits for 30 minutes before requiring an update. The router then has to send a LSR (Link State Request) to its neighbors to get an update.

Correct Answer: B. B. False
Explanation: In Distance vector routing protocols, there is a problem called count-to-infinity which occurs regularly. So, to make sure that it does not occur, the split horizon algorithm is used. There is no requirement for it in OSPF.

Correct Answer: B. B. Routing table
Explanation: The outcome of Djikstra’s calculation is the main source of entries in the routing table as it is the algorithm that is used to find the shortest path in OSPF. The calculations are done after receiving every new LSU.

Correct Answer: A. A. 89
Explanation: 89 is the IP protocol number for OSPF packets. 86 is the protocol number for DGP, 76 is the protocol number for Backroom-SATNET-Monitoring and 20 is the protocol number for Host Monitoring Protocol.

Correct Answer: D. D. Query
Explanation: LSU is the Link State Update packet, LSR is the Link State Request packet and DBD is the Database Descriptor packet in OSPF. Query packet is NOT an OSPF packet type.

Correct Answer: A. A. 224.0.0.5
Explanation: Hello protocol is used to discover neighboring routers automatically. It makes sure that the communication between neighbors is bidirectional. The multicast address that the OSPF Hello protocol uses is 224.0.0.5.

Correct Answer: A. A. True
Explanation: The Hello protocol sends periodic updates to ensure that a neighbor relationship is maintained between adjacent routers. It’s similar to the real world moral construct of saying “Hello” to initialize the communication.

Correct Answer: A. A. Exstart and exchange
Explanation: DBD stands for Database Descriptor. DBD packets are involved during the two states Exstart and Exchange. In exstart, the master and the slaves are decided and in the exchange state, the DBD is exchanged among the neighbors.