72 + Interview Questions in Network Layer in Computer Network Page 2 InterviewSolution

51.	Which field is NOT a field within an OSPF packet header?(a) Packet length(b) Router ID(c) Authentication type(d) Maxage timeI have been asked this question in quiz.I would like to ask this question from OSPF Configuration in division Network Layer of Computer Network
Answer» Correct option is (d) Maxage TIME To elaborate: The packet length FIELD gives the length of the packet in bits. The Authentication TYPE field gives the type of authentication used. The router ID field gives the ID of the source router of the packet. In an OSPF packet header, there is no field called Maxage time.

Discussion

52.	At which interval does OSPF refresh LSAs?(a) 10 seconds(b) 30 seconds(c) 30 minutes(d) 1 hourI got this question during an interview for a job.This question is from OSPF Configuration in portion Network Layer of Computer Network
Answer» Correct answer is (d) 1 HOUR To elaborate: Each LSA has its own age timer. By DEFAULT, an LSA WAITS for 30 minutes before requiring an UPDATE. So to make sure that each router first has an up-to-date LSA, OSPF REFRESHES LSAs after every 1 hour.

Discussion

53.	DBD packets are involved during which two states?(a) Exstart and exchange(b) Loading and Two-way(c) Init and Full(d) Down and LoadingI got this question in class test.My doubt stems from OSPF Configuration in portion Network Layer of Computer Network
Answer» Correct option is (a) Exstart and EXCHANGE To explain I would say: 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.

Discussion

54.	The Hello protocol sends periodic updates to ensure that a neighbor relationship is maintained between adjacent routers.(a) True(b) FalseThis question was posed to me in examination.My enquiry is from OSPF Configuration topic in division Network Layer of Computer Network
Answer» CORRECT OPTION is (a) True The best I can explain: 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.

Discussion

55.	Which multicast address does the OSPF Hello protocol use?(a) 224.0.0.5(b) 224.0.0.6(c) 224.0.0.7(d) 224.0.0.8I got this question at a job interview.This key question is from OSPF Configuration topic in portion Network Layer of Computer Network
Answer» The correct answer is (a) 224.0.0.5 The 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.

Discussion

56.	Which packet is NOT an OSPF packet type?(a) LSU(b) LSR(c) DBD(d) QueryThis question was addressed to me in a national level competition.I'm obligated to ask this question of OSPF Configuration topic in chapter Network Layer of Computer Network
Answer» Correct ANSWER is (d) Query For 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.

Discussion

57.	What is the IP protocol number for OSPF packets?(a) 89(b) 86(c) 20(d) 76I have been asked this question by my school principal while I was bunking the class.The origin of the question is OSPF Configuration in section Network Layer of Computer Network
Answer» Right OPTION is (a) 89 Easy 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.

Discussion

58.	The outcome of Dijkstra’s calculation is used to populate the __________(a) Topology table(b) Routing table(c) Neighbor table(d) Adjacency tableI have been asked this question in a job interview.My question is taken from OSPF Configuration in division Network Layer of Computer Network
Answer» Correct option is (b) Routing table Easiest 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.

Discussion

59.	Distance vector protocols use the concept of split horizon, but link-state routing protocols, such as OSPF, do not.(a) True(b) FalseThis question was addressed to me by my college professor while I was bunking the class.The doubt is from OSPF Configuration topic in division Network Layer of Computer Network
Answer» Correct option is (b) False The EXPLANATION is: 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.

Discussion

60.	Each LSA has its own age timer. By default, how long does an LSA wait before requiring an update?(a) 30 seconds(b) 1 minute(c) 30 minutes(d) 1 hourThe question was posed to me in homework.The query is from OSPF Configuration in division Network Layer of Computer Network
Answer» Correct CHOICE is (c) 30 minutes Easiest 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.

Discussion

61.	An OSPF router receives an LSA. The router checks its sequence number and finds that this number is lower than the sequence number it already has. What does the router do with the LSA?(a) ignores the LSA(b) adds it to the database(c) sends newer LSU update to source router(d) floods the LSA to the other routersI got this question in unit test.This key question is from OSPF Configuration topic in portion Network Layer of Computer Network
Answer» RIGHT choice is (c) sends newer LSU update to source ROUTER Easiest 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.

Discussion

62.	An OSPF router receives an LSA. The router checks its sequence number and finds that this number is higher than the sequence number it already has. Which two tasks does the router perform with the LSA?(a) Ignores the LSA(b) Adds it to the database(c) Sends newer LSU update to source router(d) Floods the LSA to the other routersThis question was addressed to me during a job interview.This interesting question is from OSPF Configuration in portion Network Layer of Computer Network
Answer» The correct CHOICE is (b) Adds it to the database Easiest 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.

Discussion

63.	An OSPF router receives an LSA, the router checks its sequence number, and this number matches the sequence number of the LSA that the receiving router already has. What does the receiving router do with the LSA?(a) Ignores the LSA(b) Adds it to the database(c) Sends newer LSU update to source router(d) Floods the LSA to the other routersI got this question in semester exam.The origin of the question is OSPF Configuration in portion Network Layer of Computer Network
Answer» Right OPTION is (a) IGNORES the LSA Best explanation: When the OSPF ROUTER receives an LSA, the router checks its SEQUENCE number. If this number matches the sequence number of the LSA that the receiving router already has, the router ignores the LSA.

Discussion

64.	In OSPF database descriptor packet, which field is used to detect a missing packet?(a) LSA header(b) MS(c) Database descriptor sequence number(d) OptionsI had been asked this question in an interview.The origin of the question is OSPF in chapter Network Layer of Computer Network
Answer» Correct option is (c) Database descriptor sequence NUMBER The explanation is: Sequence number field is used to detect a missing packet. The packets are to be received in ORDER of the sequence number, so if the receiver DETECTS that there is a sequence number skipped or missing in the order, it STOPS PROCESSING the further received packets and informs the sender to retransmit the packets in sequence.

Discussion

65.	In OSPF database descriptor packet, which field is used to indicate that the router is master?(a) M(b) MS(c) I(d) OptionsThe question was asked in an international level competition.My query is from OSPF topic in chapter Network Layer of Computer Network
Answer» Correct answer is (b) MS To explain: The MS bit is used to indicate if the origin of the PACKET is a master or a SLAVE. If it is set to 1, the source of the packet is a master, and if it is set to 0, the source of the packet is a slave.

Discussion

66.	In OSPF database descriptor packet, if there are more database descriptor packets in the flow, ‘M’ field is set to ____________(a) 1(b) 0(c) more(d) -1This question was addressed to me during an online interview.The above asked question is from OSPF in portion Network Layer of Computer Network
Answer» RIGHT OPTION is (a) 1 For explanation: The “M” bit is the more bit, which indicates that there are more packets to be received in the descriptor PACKET FLOW whenever it is set to 1. There is also an “I” bit which indicates if the packet is first in the flow.

Discussion

67.	In OSPF header, which field is used to detect errors in the packet?(a) Type(b) Area ID(c) Authentication type(d) ChecksumThe question was asked in an online interview.Asked question is from OSPF topic in section Network Layer of Computer Network
Answer» The correct answer is (d) CHECKSUM To elaborate: Checksum field is used to detect errors. It makes sure that the DATA portions that are being SENT are all in integrity. It can detect duplicated bits. Once an ERROR is detected, the sender has to re-transmit the data as it won’t receive an acknowledgement.

Discussion

68.	Which of the following is not a type of OSPF packet?(a) Hello(b) Link-state request(c) Link-state response(d) Link-state ACKThis question was addressed to me by my college director while I was bunking the class.I need to ask this question from OSPF topic in portion Network Layer of Computer Network
Answer» The CORRECT choice is (C) Link-state RESPONSE For explanation: The five types of OSPF packets are: Hello, Database description, Link-state request, Link-state update, and Link-state ACK. There is no Link-state response PACKET; the NEIGHBOR router sends a Link-state update packet as a response to the Link-state request packet if there is an update in the routing table.

Discussion

69.	In OSPF, which protocol is used to discover neighbour routers automatically?(a) Link state protocol(b) Error-correction protocol(c) Routing information protocol(d) Hello protocolThe question was posed to me in an interview for job.I want to ask this question from OSPF in section Network Layer of Computer Network
Answer» The correct answer is (d) Hello protocol The explanation is: Hello protocol is used to discover neighboring routers automatically. It MAKES sure that the communication between neighbors is bidirectional. It’s SIMILAR to the real WORLD moral CONSTRUCT of saying “Hello” to INITIALIZE the communication.

Discussion

70.	Which of the following is false with respect to the features of OSPF?(a) Support for fixed-length subnetting by including the subnet mask in the routing message(b) More flexible link cost than can range from 1 to 65535(c) Use of designated router(d) Distribution of traffic over multiple paths that have equal cost to the destinationThe question was asked at a job interview.I'm obligated to ask this question of OSPF in chapter Network Layer of Computer Network
Answer» Right CHOICE is (a) Support for fixed-length subnetting by INCLUDING the subnet mask in the routing message The explanation is: OSPF provides support for variable-length sunbathing by including the subnet mask in the routing message. For fixed length SUBNETS, there is no REQUIREMENT for including the subnet mask in the routing message as there is just one subnet mask for all the subnets.

Discussion

71.	The computation of the shortest path in OSPF is usually done by ____________(a) Bellman-ford algorithm(b) Routing information protocol(c) Dijkstra’s algorithm(d) Distance vector routingThis question was addressed to me during an interview.I'd like to ask this question from OSPF topic in section Network Layer of Computer Network
Answer» The correct choice is (c) Dijkstra’s algorithm Easiest EXPLANATION: Shortest path in OSPF is usually COMPUTED by Dijkstra’s algorithm. It was PROPOSED by Edsger W. Dijkstra in the year 1956. It is a greedy method algorithm and HENCE may not guarantee the shortest path every time, but is really fast.

Discussion

72.	Open Shortest Path First (OSPF) is also called as _____________(a) Link state protocol(b) Error-correction protocol(c) Routing information protocol(d) Border gateway protocolThis question was posed to me in exam.This is a very interesting question from OSPF topic in section Network Layer of Computer Network
Answer» The correct OPTION is (a) Link state protocol The best explanation: In OSPF, the link state of each path is checked, and then the shortest path is chosen among only the open state links. Each OSPF router monitors the COST of the link to each of its neighbors and then FLOODS the link state information to other ROUTERS in the network.

Discussion

Explore topic-wise InterviewSolutions in .

Which field is NOT a field within an OSPF packet header?(a) Packet length(b) Router ID(c) Authentication type(d) Maxage timeI have been asked this question in quiz.I would like to ask this question from OSPF Configuration in division Network Layer of Computer Network

At which interval does OSPF refresh LSAs?(a) 10 seconds(b) 30 seconds(c) 30 minutes(d) 1 hourI got this question during an interview for a job.This question is from OSPF Configuration in portion Network Layer of Computer Network

DBD packets are involved during which two states?(a) Exstart and exchange(b) Loading and Two-way(c) Init and Full(d) Down and LoadingI got this question in class test.My doubt stems from OSPF Configuration in portion Network Layer of Computer Network

The Hello protocol sends periodic updates to ensure that a neighbor relationship is maintained between adjacent routers.(a) True(b) FalseThis question was posed to me in examination.My enquiry is from OSPF Configuration topic in division Network Layer of Computer Network

Which multicast address does the OSPF Hello protocol use?(a) 224.0.0.5(b) 224.0.0.6(c) 224.0.0.7(d) 224.0.0.8I got this question at a job interview.This key question is from OSPF Configuration topic in portion Network Layer of Computer Network

Which packet is NOT an OSPF packet type?(a) LSU(b) LSR(c) DBD(d) QueryThis question was addressed to me in a national level competition.I'm obligated to ask this question of OSPF Configuration topic in chapter Network Layer of Computer Network

What is the IP protocol number for OSPF packets?(a) 89(b) 86(c) 20(d) 76I have been asked this question by my school principal while I was bunking the class.The origin of the question is OSPF Configuration in section Network Layer of Computer Network

The outcome of Dijkstra’s calculation is used to populate the __________(a) Topology table(b) Routing table(c) Neighbor table(d) Adjacency tableI have been asked this question in a job interview.My question is taken from OSPF Configuration in division Network Layer of Computer Network

Each LSA has its own age timer. By default, how long does an LSA wait before requiring an update?(a) 30 seconds(b) 1 minute(c) 30 minutes(d) 1 hourThe question was posed to me in homework.The query is from OSPF Configuration in division Network Layer of Computer Network

In OSPF database descriptor packet, which field is used to detect a missing packet?(a) LSA header(b) MS(c) Database descriptor sequence number(d) OptionsI had been asked this question in an interview.The origin of the question is OSPF in chapter Network Layer of Computer Network

In OSPF database descriptor packet, which field is used to indicate that the router is master?(a) M(b) MS(c) I(d) OptionsThe question was asked in an international level competition.My query is from OSPF topic in chapter Network Layer of Computer Network

In OSPF database descriptor packet, if there are more database descriptor packets in the flow, ‘M’ field is set to ____________(a) 1(b) 0(c) more(d) -1This question was addressed to me during an online interview.The above asked question is from OSPF in portion Network Layer of Computer Network

In OSPF header, which field is used to detect errors in the packet?(a) Type(b) Area ID(c) Authentication type(d) ChecksumThe question was asked in an online interview.Asked question is from OSPF topic in section Network Layer of Computer Network

Which of the following is not a type of OSPF packet?(a) Hello(b) Link-state request(c) Link-state response(d) Link-state ACKThis question was addressed to me by my college director while I was bunking the class.I need to ask this question from OSPF topic in portion Network Layer of Computer Network