Category: Computer Networks Objective Questions

Computer Networks Multiple Choice Questions on “Physical Media”.

1. Which of this is not a guided media?
a) Fiber optical cable
b) Coaxial cable
c) Wireless LAN
d) Copper wire

Answer: c
Clarification: Wireless LAN is unguided media.

2. UTP is commonly used in __________
a) DSL
b) FTTP
c) HTTP
d) None of the mentioned

Answer: a
Clarification: Unshielded twisted pair(UTP) is commonly used in home access.

3. Coaxial cable consists of _______ concentric copper conductors.
a) 1
b) 2
c) 3
d) 4

Answer: b
Clarification: Coaxial cable has an inner conductor surrounded by a insulating layer, which is surrounded by a conducting shield. Coaxial cable is used to carry high frequency signals with low losses.

4. Fiber optics posses following properties __________
a) Immune electromagnetic interference
b) Very less signal attenuation
c) Very hard to tap
d) All of the mentioned

Answer: d
Clarification: In fibre optics the transmission of information is in the form of light or photons. Due to all above properties mentioned in options fibre optics can be submerged in water and are used at more risk environments.

5. If an Optical Carrier is represented as OC-n, generally the link speed equals(in Mbps) __________
a) n*39.8
b) n*51.8
c) 2n*51.8
d) None of the mentioned

Answer: b
Clarification: The base unit of transmission rates in optical fibre is 51.8 Mbits/s. So an optical carrier represented as OC-n has n*51.8 Mbits/s transmission speed. For eg. OC-3 has 3*51.8 Mbits/s speed.

6. Terrestrial radio channels are broadly classifed into _____ groups.
a) 2
b) 3
c) 4
d) 1

Answer: b
Clarification: The three types are those that operate over very short distance, those that operate in local areas, those that operate in the wide area.

7. Radio channels are attractive medium because __________
a) Can penetrate walls
b) Connectivity can be given to mobile user
c) Can carry signals for long distance
d) All of the mentioned

Answer: d
Clarification: Radio channels can penetrate walls, can be used to provide connectivity to mobile users and can also carry signals for long distances.

8. Geostationary satellites ___________
a) Are placed at a fixed point above the earth
b) Rotate the earth about a fixed axis
c) Rotate the earth about a varying axis
d) All of the mentioned

Answer: a
Clarification: They are placed in orbit at 36,000km above Earth’s surface.

Computer Networks Multiple Choice Questions on “Telnet”.

1. The application layer protocol used by a Telnet application is ________
a) Telnet
b) FTP
c) HTTP
d) SMTP

Answer: a
Clarification: Telnet is an application layer protocol that provides access to the command-line interface on a remote host. Telnet stands for teletype network.

2. Which amongst the following statements is correct for “character at a time” mode?
a) Character processing is done on the local system under the control of the remote system
b) Most text typed is immediately sent to the remote host for processing
c) All text is echoed locally, only completed lines are sent to the remote host
d) All text is processed locally, and only confirmed lines are sent to the remote host

Answer: b
Clarification: In character at a time mode, the typed text is sent immediately to the remote host while the user is typing. Another mode used in Telnet is “Old line by line” mode in which only completed lines are sent to the remote host.

3. _______ allows you to connect and login to a remote computer
a) Telnet
b) FTP
c) HTTP
d) SMTP

Answer: a
Clarification: Telnet provides access to the command-line interface on a remote computer. One can login to the computer from the command-line interface.

4. What is the correct syntax to be written in the web browser to initiate a Telnet connection to www..com?
a) telnet//www..com
b) telnet:www..com
c) telnet://www..com
d) telnet www..com

Answer: c
Clarification: telnet://” is the header to be used to initiate a Telnet connection to a web server. One can browse the website using telnet if they are authorized to.

5. Telnet is used for _______
a) Television on net
b) Network of Telephones
c) Remote Login
d) Teleshopping site

Answer: c
Clarification: Telnet is an application layer protocol that provides access to the command line interface of a remote computer that can be used to perform remote login.

6. Which one of the following is not correct?
a) telnet is a general purpose client-server program
b) telnet lets user access an application on a remote computer
c) telnet can also be used for file transfer
d) telnet can be used for remote login

Answer: c
Clarification: File Transfer Protocol is used for file transfer. Telnet provides access to the command-line interface on a remote host.

7. Which operating mode of telnet is full duplex?
a) default mode
b) server mode
c) line mode
d) character mode

Answer: c
Clarification: In line mode, terminal character processing is done on the client side but editing is enabled on the server side. Line mode reduces the number of packets and is useful for long delay networks.

8. If we want that a character be interpreted by the client instead of server _________
a) interpret as command (IAC) escape character has to be used
b) control functions has to be disabled
c) it is not possible
d) cli character has to be used

Answer: a
Clarification: The client must look at each byte that arrives and look for IAC escape character. If IAC is found, the client moves on to look for any other code or IAC. If the next byte is IAC – a single byte is presented by the client to the terminal. If IAC is followed by any other code than IAC, the client interprets this as a command.

Computer Networks Multiple Choice Questions on “ICMP”.

1. Internet Control Message Protocol (ICMP) has been designed to compensate _________
a) Error-reporting
b) Error-correction
c) Host and management queries
d) All of the mentioned

Answer: d
Clarification: IP by itself does not provide the features of error reporting or error correction. So, to address these issues a network layer protocol called Internet Control Message Protocol is used. ICMP operates over the IP packet to provide error reporting functionality.

2. Header size of the ICMP message is _________
a) 8-bytes
b) 8-bits
c) 16-bytes
d) 16-bits

Answer: a
Clarification: An ICMP message has an 8-byte header and a variable size data section. Out of the 8 bytes, the first 4 bytes are of a fixed format having the type, code and checksum fields and the next 4 bytes depend upon the type of the message.

3. During error reporting, ICMP always reports error messages to ________
a) Destination
b) Source
c) Next router
d) Previous router

Answer: b
Clarification: ICMP notifies the source about the error when an error is detected because the datagram knows information about source and destination IP address. The source can then retransmit the data again or try to correct those errors.

4. Which of these is not a type of error-reporting message?
a) Destination unreachable
b) Source quench
c) Router error
d) Time exceeded

Answer: c
Clarification: Router error is not a type of error-reporting message in ICMP. The type of error reporting message is specified in the ICMP header. Destination unreachable is type 3 error message, source quench is type 4, and time exceeded is type 11 error message.

5. ICMP error message will not be generated for a datagram having a special address such as _______
a) 127.0.0.0
b) 12.1.2
c) 11.1
d) 127

Answer: a
Clarification: 127.0.0.0 is a special address known as the loopback address which is used for testing purpose of a machine without actually communicating with a network. Thus no error reporting message will be generated for such special addresses.

6. When a router cannot route a datagram or host cannot deliver a datagram, the datagram is discarded and the router or the host sends a ____________ message back to the source host that initiated the datagram.
a) Destination unreachable
b) Source quench
c) Router error
d) Time exceeded

Answer: a
Clarification: Router sends destination unreachable message if the destination is not found. Destination unreachable is type 3 error reporting message. It is invoked when the router can’t find a path to the intended destination to forward the packet through.

7. The source-quench message in ICMP was designed to add a kind of ____________ to the IP.
a) error control
b) flow control
c) router control
d) switch control

Answer: b
Clarification: Firstly, it informs the source that the datagram has been discarded. Secondly, it warns the source that there is congestion in the network. It’s type 4 error reporting message after which the source is expected to reduce the flow of packets.

8. In case of time exceeded error, when the datagram visits a router, the value of time to live field is _________
a) Remains constant
b) Decremented by 2
c) Incremented by 1
d) Decremented by 1

Answer: d
Clarification: This field will be decremented by 1 at every router, and will be zero by the time it reaches source. This error reporting message is type 11 and is used to prevent the router from travelling forever in case some unknown path anomaly occurs.

9. Two machines can use the timestamp request and timestamp replay messages to determine the ___________ needed for an IP datagram to travel between them.
a) Half-trip time
b) Round-trip time
c) Travel time for the next router
d) Time to reach the destination/source

Answer: b
Clarification: The round-trip time refers to the total time taken combining the time taken for a packet sent from a source to reach a destination and the time taken the acknowledgement sent by the destination to reach the source. The Router sends destination unreachable message if the destination is not found.

10. During debugging, we can use the ____________ program to find if a host is alive and responding.
a) traceroute
b) shell
c) ping
d) java

Answer: c
Clarification: Ping program is used to find if a host is alive and responding. It is to be entered into a command line with the syntax “ping (IP address)” to be executed. Traceroute is a program used to find the shortest route to the destination IP.

11. In windows ____________ can be used to trace the route of the packet from the source to the destination.
a) traceroute
b) tracert
c) ping
d) locater

Answer: b
Clarification: Tracert is used in case of windows, whereas Traceroute in UNIX. Tracert is a program used to find the shortest route to the destination IP. The Router sends destination unreachable message if a path to the destination IP is not found.

12. In a simple echo-request message, the value of the sum is 01010000 01011100. Then, value of checksum is ___________
a) 10101111 10100011
b) 01010000 01011100
c) 10101111 01011100
d) 01010000 10100011

Answer: a
Clarification: The sender side adds the bits of the fragmented packet to find a sum. Checksum is the compliment of the sum (exchange 0’s and 1’s). The receiver then has to verify the checksum by adding the bits of the received packet to ensure that the packet is error-free.

Computer Networks online quiz on “OSPF Configuration”.

1. 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 routers

Answer: a
Clarification: 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.

2. 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 routers

Answer: b
Clarification: 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.

3. 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 routers

Answer: c
Clarification: 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.

4. 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 hour

Answer: c
Clarification: 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.

5. Distance vector protocols use the concept of split horizon, but link-state routing protocols, such as OSPF, do not.
a) True
b) False

Answer: b
Clarification: 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.

6. The outcome of Dijkstra’s calculation is used to populate the __________
a) Topology table
b) Routing table
c) Neighbor table
d) Adjacency table

Answer: b
Clarification: 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.

7. What is the IP protocol number for OSPF packets?
a) 89
b) 86
c) 20
d) 76

Answer: a
Clarification: 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.

8. Which packet is NOT an OSPF packet type?
a) LSU
b) LSR
c) DBD
d) Query

Answer: d
Clarification: 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.

9. 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) 224.0.0.8

Answer: a
Clarification: 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.

10. The Hello protocol sends periodic updates to ensure that a neighbor relationship is maintained between adjacent routers.
a) True
b) False

Answer: a
Clarification: 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.

11. DBD packets are involved during which two states?
a) Exstart and exchange
b) Loading and Two-way
c) Init and Full
d) Down and Loading

Answer: a
Clarification: 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.

12. At which interval does OSPF refresh LSAs?
a) 10 seconds
b) 30 seconds
c) 30 minutes
d) 1 hour

Answer: d
Clarification: 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.

13. Which field is NOT a field within an OSPF packet header?
a) Packet length
b) Router ID
c) Authentication type
d) Maxage time

Answer: d
Clarification: 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.

14. Which two commands are required for basic OSPF configuration?
a) “[Network mask] area [area-id]” and “Router ospf [process-id]”
b) “[Wildcard-mask] area [area-id]” and “[Network mask] area [area-id]”
c) Only “Router ospf [process-id]”
d) “[Wildcard-mask] area [area-id]” and “Router ospf [process-id]”

Answer: d
Clarification: The “Router ospf [process-id]” command enables OSPF routing protocol in the router and the “[Wildcard-mask] area [area-id]” command is used to select the interfaces that we want to include in the OSPF process. That is enough for the basic configuration of OSPF in a router.

15. Which OSPF show command describes a list of OSPF adjacencies?
a) Show ip ospf interface
b) Show ip ospf
c) Show ip route
d) Show ip ospf neighbor

Answer: d
Clarification: The “Show ip ospf neighbor” command is the OSPF show command that can describe a list of OSPF adjacencies i.e. the list of adjacent nodes or neighbors. The router will only communicate with its neighbors directly.

Computer Networks Multiple Choice Questions on “Packet Switching & Circuit Switching”.

1. A local telephone network is an example of a _______ network.
a) Packet switched
b) Circuit switched
c) Bit switched
d) Line switched

Answer: b
Clarification: Circuit switching is connection oriented switching technique, whereas in the case of packet switching, it is connectionless. Circuit switching is implemented in the Physical layer, whereas packet switching is implemented in the Network layer. Internet too is based on the concept of circuit switching.

2. Most packet switches use this principle ____________
a) Stop and wait
b) Store and forward
c) Store and wait
d) Stop and forward

Answer: b
Clarification: The packet switch will not transmit the first bit to outbound link until it receives the entire packet. If the entire packet is not received and the time-out period expires, the packet switch will inform the sender to resend the part of packet or the entire packet based on the algorithm being used.

3. If there are N routers from source to destination, the total end to end delay in sending packet P(L-> number of bits in the packet R-> transmission rate) is equal to ______________
a) N
b) (N*L)/R
c) (2N*L)/R
d) L/R

Answer: b
Clarification: The equation to find the end to end delay when no. of bits, transmission rate and no. of routers is given by (N*L)/R. The total end to end delay, that is, nodal delay is the sum of all, the processing delay, queuing delay, transmission delay and propagation delay.

4. What are the Methods to move data through a network of links and switches?
a) Packet switching and Line switching
b) Circuit switching and Line switching
c) Line switching and bit switching
d) Packet switching and Circuit switching

Answer: d
Clarification: Packet switching and Circuit switching are two different types of switching methods used to connect the multiple communicating devices with one another. Packet switching is used in conventional LAN systems and circuit switching is used in telephonic systems.

5. The required resources for communication between end systems are reserved for the duration of the session between end systems in ________ method.
a) Packet switching
b) Circuit switching
c) Line switching
d) Frequency switching

Answer: b
Clarification: In circuit switching, a physical path between the sender and receiver is established. This path is maintained until the connection is needed. Circuit switching is implemented in the Physical layer and is used in telephonic systems.

6. As the resources are reserved between two communicating end systems in circuit switching, ___________ is achieved.
a) authentication
b) guaranteed constant rate
c) reliability
d) store and forward

Answer: b
Clarification: Circuit switching is connection oriented and is always implemented in the physical layer. Once a path is set, all transmission occurs through the same path. It is used since the early times in telephonic systems.

7. In _________ systems, resources are allocated on demand.
a) packet switching
b) circuit switching
c) line switching
d) frequency switching

Answer: a
Clarification: In packet switching, the bits are received in out of order and need to be assembled at the receiver end, whereas in the case of Circuit switching, all the bits are received in order. All transmissions may not occur through the same path in case of packet switching.

8. Which of the following is not an application layer service?
a) Network virtual terminal
b) File transfer, access, and management
c) Mail service
d) Error control

Answer: d
Clarification: Application layer is the topmost layer in the OSI model. Network virtual terminal, mail service, file transfer, access and management are all services of the application layer. It uses protocols like HTTP, FTP, and DNS etc. to provide these services.

Computer Networks Multiple Choice Questions on “Telnet”.

1. Telnet protocol is used to establish a connection to __________
a) TCP port number 21
b) TCP port number 22
c) TCP port number 23
d) TCP port number 25

Answer: c
Clarification: TCP port 21 is used for FTP, TCP port 22 is used for SSH and TCP port 25 is used for SMTP. Telnet provides access to a command line interface on a remote computer using the TCP port number 23.

2. Which one of the following is not true?
a) telnet defines a network virtual terminal (NVT) standard
b) client programs interact with NVT
c) server translates NVT operations
d) client can transfer files using to remote server using NVT

Answer: d
Clarification: The client can use the NVT only to interact with the programs already present on the remote server, not to transfer files to it. To transfer files, an FTP connection has to be used.

3. All telnet operations are sent as ________
a) 4 bits
b) 8 bits
c) 16 bits
d) 32 bits

Answer: b
Clarification: Telnet provides a bi-directional, 8-bit byte oriented communications facility through which operations are sent as 8-bit bytes for the server to interpret.

4. AbsoluteTelnet is a telnet client for _______ Operating system.
a) windows
b) linux
c) mac
d) ubuntu

Answer: a
Clarification: AbsoluteTelnet was originally released in 1999. It was developed by Brian Pence of Celestial Software.

5. The decimal code of Interpret as Command (IAC) character is _______
a) 252
b) 253
c) 254
d) 255

Answer: d
Clarification: If we want that a character be interpreted by the client instead of server, we use the IAC character. If IAC is followed by any other code than IAC, the client interprets it as a character.

6. Which of the following is true for character mode operation of telnet implementation?
a) each character typed is sent by the client to the server
b) each character typed is discarded by the server
c) each character typed is aggregated into a word and then sent to the server
d) each character type is aggregated into a line and then sent to the server

Answer: a
Clarification: In character mode, each character that the user is typing is immediately sent to the server which then interprets it only after the complete operation command is received.

7. In which mode of telnet, the client echoes the character on the screen but does not send it until a whole line is completed?
a) default mode
c) character mode
c) server mode
d) command mode

Answer: a
Clarification: In the default mode, the client does not send each character typed by the user to the server, thus saving the amount of packet transmissions required for executing each operation. But the server has to remain idle until the client sends the completed line wasting a lot of time.

8. Which one of the following is not correct?
a) telnet is a general purpose client-server program
b) telnet lets user access an application on a remote computer
c) telnet can also be used for file transfer
d) telnet can be used for remote login

Answer: c
Clarification: File Transfer Protocol is used for file transfer. Telnet provides access to the command-line interface on a remote host.