Category: Computer Networks Objective Questions

Computer Networks Multiple Choice Questions & Answers on “RIP v2”.

1. Which statement is true regarding classless routing protocols?
a) The use of discontinuous networks is not allowed
b) The use of variable length subnet masks is permitted
c) RIPv1 is a classless routing protocol
d) RIPv2 supports classless routing

Answer: b
Clarification: Classful routing means that all hosts in the internetwork use the same mask. Classless routing means that you can use Variable Length Subnet Masks (VLSMs) and can also support discontinuous networking.

2. What is route poisoning?
a) It sends back the protocol received from a router as a poison pill, which stops the regular updates. The use of variable length subnet masks is permitted
b) It is information received from a router that can’t be sent back to the originating router.RIPv2 supports classless routing
c) It prevents regular update messages from reinstating a route that has just come up
d) It describes when a router sets the metric for a downed link to infinity

Answer: d
Clarification: When a network goes down, the distance-vector routing protocol initiates route poisoning by advertising the network with a metric of 16, or unreachable.

3. Which of the following is true regarding RIPv2?
a) It has a lower administrative distance than RIPv1
b) It converges faster than RIPv1
c) It has the same timers as RIPv1
d) It is harder to configure than RIPv1

Answer: c
Clarification: RIPv2 is pretty much just like RIPv1. It has the same administrative distance and timers and is configured just like RIPv1.

4. Which of the situations might not require multiple routing protocols in a network?
a) When a new Layer 2-only switch is added to the network
b) When you are migrating from one routing protocol to another
c) When you are using routers from multiple vendors
d) When there are host-based routers from multiple vendors

Answer: a
Clarification: Multiple routing protocols are required only when we need to migrate from one routing protocol to another, or when we are using routers from multiple vendors, or when there are host-based routers from multiple vendors. Routing is not a layer-2 function so we don’t require multiple routing protocols when new layer-2 switch is added.

5. Which two routing protocols can be redistributed into OSPF by a Cisco router?
a) IP EIGRP and AppleTalk EIGRP
b) AppleTalk EIGRP and RIPv2
c) RIPv2 and IP EIGRP
d) IPX RIP & AppleTalk EIGRP

Answer: c
Clarification: OSPF stands for Open Shortest Path First. It is a Link state routing protocol. IP EIGRP and RIPv2 can be redistributed into OSPF by a Cisco router.

6. Which is a reason for avoiding doing route redistribution on two routers between the same two routing domains?
a) Higher cost of two routers
b) Routing feedback
c) Cisco IOS incompatibility
d) Not possible to use two routers

Answer: b
Clarification: Routing feedback is an anomaly in which the routing protocols go back and forth between one route and another. Routing feedback is a reason for avoiding doing route redistribution on two routers between the same two routing domains.

7. What does administrative distance rank?
a) Metrics
b) Sources of routing information
c) Router reliability
d) Best paths

Answer: b
Clarification: Sources of routing information is the administrative distance rank. It is used by routers to select the best path when there are different routes to the same destination. It’s used only two different routing protocols are being used.

8. Which protocol maintains neighbor adjacencies?
a) RIPv2 and EIGRP
b) IGRP and EIGRP
c) RIPv2
d) EIGRP

Answer: c
Clarification: Neighbor adjacency refers to the formal handshake performed by neighboring routers. It is to be done before the router share any routing information. RIP V2 maintains neighbor adjacencies.

9. Which routing protocol implements the diffusing update algorithm?
a) IS-IS
b) IGRP
c) EIGRP
d) OSPF

Answer: c
Clarification: The diffusing update algorithm (DUAL) is used to maintain backup routes to a destination for when the primary route fails. EIGRP routing protocol implements the diffusing update algorithm.

10. Which protocol should you select if the network diameter is more than 17 hops?
a) RIPv1
b) RIPv2
c) EIGRP
d) OSPF

Answer: b
Clarification: RIPv2protocol should you select if the network diameter is more than 17 hops. It uses classless routing and the routing updates are broadcasted over the network. It notifies routers about the update so that they update their own routing tables.

Computer Networks Multiple Choice Questions on “Data Link Layer”.

1. The data link layer takes the packets from _________ and encapsulates them into frames for transmission.
a) network layer
b) physical layer
c) transport layer
d) application layer

Answer: a
Clarification: In computer networks, the data from application layer is sent to transport layer and is converted to segments. These segments are then transferred to the network layer and these are called packets. These packets are then sent to data link layer where they are encapsulated into frames. These frames are then transferred to physical layer where the frames are converted to bits. Error control and flow control data is inserted in the frames at the data link layer.

2. Which of the following tasks is not done by data link layer?
a) framing
b) error control
c) flow control
d) channel coding

Answer: d
Clarification: Channel coding is the function of physical layer. Data link layer mainly deals with framing, error control and flow control. Data link layer is the layer where the packets are encapsulated into frames.

3. Which sublayer of the data link layer performs data link functions that depend upon the type of medium?
a) logical link control sublayer
b) media access control sublayer
c) network interface control sublayer
d) error control sublayer

Answer: b
Clarification: Media access control (MAC) deals with transmission of data packets to and from the network-interface card, and also to and from another remotely shared channel. The MAC sublayer also prevents collision using protocols like CSMA/CD.

4. Header of a frame generally contains ______________
a) synchronization bytes
b) addresses
c) frame identifier
d) all of the mentioned

Answer: d
Clarification: In a frame, the header is a part of the data that contains all the required information about the transmission of the file. It contains information like synchronization bytes, addresses, frame identifier etc. It also contains error control information for reducing the errors in the transmitted frames.

5. Automatic repeat request error management mechanism is provided by ________
a) logical link control sublayer
b) media access control sublayer
c) network interface control sublayer
d) application access control sublayer

Answer: a
Clarification: The logical link control is a sublayer of data link layer whose main function is to manage traffic, flow and error control. The automatic repeat request error management mechanism is provided by the LLC when an error is found in the received frame at the receiver’s end to inform the sender to re-send the frame.

6. When 2 or more bits in a data unit has been changed during the transmission, the error is called ____________
a) random error
b) burst error
c) inverted error
d) double error

Answer: b
Clarification: When a single bit error occurs in a data, it is called single bit error. When more than a single bit of data is corrupted or has error, it is called burst error. If a single bit error occurs, the bit can be simply repaired by inverting it, but in case of a burst error, the sender has to send the frame again.

7. CRC stands for __________
a) cyclic redundancy check
b) code repeat check
c) code redundancy check
d) cyclic repeat check

Answer: a
Clarification: Cyclic redundancy check is a code that is added to a data which helps us to identify any error that occurred during the transmission of the data. CRC is only able to detect errors, not correct them. CRC is inserted in the frame trailer.

8. Which of the following is a data link protocol?
a) ethernet
b) point to point protocol
c) hdlc
d) all of the mentioned

Answer: d
Clarification: There are many data link layer protocols. Some of them are SDLC (synchronous data link protocol), HDLC (High level data link control), SLIP (serial line interface protocol), PPP (Point to point protocol) etc. These protocols are used to provide the logical link control function of the Data Link Layer.

9. Which of the following is the multiple access protocol for channel access control?
a) CSMA/CD
b) CSMA/CA
c) Both CSMA/CD & CSMA/CA
d) HDLC

Answer: c
Clarification: In CSMA/CD, it deals with detection of collision after collision has occurred, whereas CSMA/CA deals with preventing collision. CSMA/CD is abbreviation for Carrier Sensing Multiple Access/Collision detection. CSMA/CA is abbreviation for Carrier Sensing Multiple Access/Collision Avoidance. These protocols are used for efficient multiple channel access.

10. The technique of temporarily delaying outgoing acknowledgements so that they can be hooked onto the next outgoing data frame is called ____________
a) piggybacking
b) cyclic redundancy check
c) fletcher’s checksum
d) parity check

Answer: a
Clarification: Piggybacking is a technique in which the acknowledgment is temporarily delayed so as to be hooked with the next outgoing data frame. It saves a lot of channel bandwidth as in non-piggybacking system, some bandwidth is reserved for acknowledgement.

Computer Networks Multiple Choice Questions on “SMTP”.

1. Simple mail transfer protocol (SMTP) utilizes _________ as the transport layer protocol for electronic mail transfer.
a) TCP
b) UDP
c) DCCP
d) SCTP

Answer: a
Clarification: Since TCP is a reliable protocol, it’s more efficient to use TCP protocol for e-mail transfer. TCP also provides more security than other transport layer protocols.

2. SMTP connections secured by SSL are known as _____________
a) SMTPS
b) SSMTP
c) SNMP
d) STARTTLS

Answer: a
Clarification: SSMTP is a simple mail transfer program to send mail from a local PC to a mail host. SNMP is a network management protocol. STARTTLS connections are secured by TLS.

3. SMTP uses which of the following TCP port?
a) 22
b) 23
c) 21
d) 25

Answer: d
Clarification: Port 21 is used for FTP control connection, port 22 is used by SSH, and port 23 is used by TELNET.

4. Which one of the following protocol is used to receive mail messages?
a) SMTP
b) Post Office Protocol (POP)
c) Internet Message Access Protocol (IMAP)
d) FTP

Answer: d
Clarification: FTP is used to share files. SMTP, POP and IMAP are the protocols used to send and receive mails on the internet.

5. What is on-demand mail relay (ODMR)?
a) protocol for SMTP security
b) an SMTP extension
c) protocol for web pages
d) protocol for faster mail transfer

Answer: b
Clarification: ODMR is an extension to SMTP, in which mails are relayed to the receivers after they are authenticated. It allows only the authorized receivers to receive the mail.

6. An email client needs to know the _________ of its initial SMTP server.
a) IP address
b) MAC address
c) URL
d) Name

Answer: a
Clarification: The client needs to know the IP of its initial SMTP server as it has to send the mail first to that server and then the server forwards the mail ahead on behalf of the user.

7. An SMTP session may not include _______
a) zero SMTP transaction
b) one SMTP transaction
c) more than one SMTP transaction
d) one HTTP transaction

Answer: d
Clarification: An SMTP session can only include SMTP transactions regardless the number. Any other protocol’s transaction is not included in an SMTP session.

8. SMTP defines _______
a) message transport
b) message encryption
c) message content
d) message password

Answer: a
Clarification: As the name suggests, Simple Mail Transfer Protocol is only responsible for “how” the message is transferred i.e. Transport of the message. Other protocols such as TCP are used to provide other services like encryption for the messages.

9. Which one of the following is an SMTP server configured in such a way that anyone on the internet can send e-mail through it?
a) open mail relay
b) wide mail reception
c) open mail reception
d) short mail reception

Answer: a
Clarification: Anyone can send an e-mail through an Open Mail Relay server so it acted like a free relay for email agents to forward their mails through. Open Mail Relays are now unpopular because they can be used by attackers to perform man-in-the-middle attacks.

10. SMTP is not used to deliver messages to ______
a) user’s terminal
b) user’s mailbox
c) user’s word processor
d) user’s email client

Answer: c
Clarification: SMTP can only be used to send messages to user’s terminal, email client or mailbox. A stand-alone word processor cannot be connected to a network, so it won’t be possible to deliver messages to it.

Computer Networks Multiple Choice Questions on “ATM & Frame Relay”.

1. ATM and frame relay are ________
a) virtual circuit networks
b) datagram networks
c) virtual private networks
d) virtual public networks

Answer: a
Clarification: ATM and frame relay are transmission modes in which information is transferred through electric circuit layer as packets. ATM has fixed packet size and frame relay has variable packet size.

2. ATM uses _______________
a) asynchronous frequency division multiplexing
b) asynchronous time division multiplexing
c) asynchronous space division multiplexing
d) asynchronous amplitude division multiplexing

Answer: b
Clarification: ATM uses a constant data stream consisting of transmission cells to transmit information in a fixed division of time. The packet size remains fixed.

3. ATM standard defines _______ layers.
a) 2
b) 3
c) 4
d) 5

Answer: b
Clarification: The three layers are physical layer, ATM layer and application adoption layer. The physical layer corresponds to the physical layer, ATM layer corresponds to the data link layer and the AAL layer corresponds to the network layer of the OSI model.

4. ATM can be used for ________
a) local area network
b) wide area network
c) campus area network
d) networks covering any range

Answer: d
Clarification: ATM is a connection oriented network for cell relay which can be implemented for networks covering any area. It uses Time Division Multiplexing and supports voice, video and data communications.

5. An ATM cell has the payload field of __________
a) 32 bytes
b) 48 bytes
c) 64 bytes
d) 128 bytes

Answer: b
Clarification: An ATM field contains a header and a payload. The header is of 5 bytes and the payload is of 48 bytes. The size of the header remains fixed.

6. Frame relay has error detection at the ______
a) physical layer
b) data link layer
c) network layer
d) transport layer

Answer: b
Clarification: The Frame Relay header contains an 8-bit Header Error Control field (HEC). The HEC field contains an 8-bit CRC which is used for error control.

7. Virtual circuit identifier in frame relay is called ______
a) data link connection identifier
b) frame relay identifier
c) cell relay identifier
d) circuit connection identifier

Answer: a
Clarification: The Data Link Connection Identifier is 10-bit virtual circuit identifier. It is used to assign frames to the specified Permanent Virtual Circuits or Switched Virtual Circuits.

8. Frame relay has _______
a) only physical layer
b) only data link layer
c) only network layer
d) both physical and data link layer

Answer: d
Clarification: The physical layer is guided by the protocols recognized by the ANSI. The data link layer supports the simplified core functions specified by the OSI model.

9. In frame relay networks, extended address is used _______
a) to increase the range of data link connection identifiers
b) for error detection
c) for encryption
d) for error recovery

Answer: a
Clarification: Extended address is indicated by the last bit of every address byte in the DLCI. It specifies whether the byte is the last in the addressing field. It is used to increase the range of data link connection identifiers.

10. What is FRAD in frame relay network?
a) FRAD assembles and disassembles the frames coming from other protocols
b) FRAD is used for modulation and demodulation
c) FRAD is used for error detection
d) FRAD is used for error recovery

Answer: a
Clarification: FRAD stands for Frame Relay Assembler/Disassembler. It converts packets into frames that can be transmitted over Frame Relay Networks. It operates at the physical layer.

Computer Networks Multiple Choice Questions on “Cryptography”.

1. In cryptography, what is cipher?
a) algorithm for performing encryption and decryption
b) encrypted message
c) both algorithm for performing encryption and decryption and encrypted message
d) decrypted message

Answer: a
Clarification: Cipher is a method to implement encryption and decryption of messages travelling in a network. It’s used to increase the confidentiality of the messages.

2. In asymmetric key cryptography, the private key is kept by __________
a) sender
b) receiver
c) sender and receiver
d) all the connected devices to the network

Answer: b
Clarification: The private key is kept only by the receiver of the message. Its aim is to make sure that only the intended receiver can decipher the message.

3. Which one of the following algorithm is not used in asymmetric-key cryptography?
a) rsa algorithm
b) diffie-hellman algorithm
c) electronic code book algorithm
d) dsa algorithm

Answer: c
Clarification: Electronic code book algorithm is a block cipher method in which each block of text in an encrypted message corresponds to a block of data. It is not feasible for block sizes smaller than 40 bits.

4. In cryptography, the order of the letters in a message is rearranged by __________
a) transpositional ciphers
b) substitution ciphers
c) both transpositional ciphers and substitution ciphers
d) quadratic ciphers

Answer: a
Clarification: In transposition ciphers, the order of letters in a plaintext message is shuffled using a pre-defined method. Some of such ciphers are Rail fence cipher and Columnar transposition.

5. What is data encryption standard (DES)?
a) block cipher
b) stream cipher
c) bit cipher
d) byte cipher

Answer: a
Clarification: DES is a symmetric key block cipher in which the block size is 64 bits and the key size is 64 bits. It is vulnerable to some attacks and is hence not that popularly used.

6. Cryptanalysis is used __________
a) to find some insecurity in a cryptographic scheme
b) to increase the speed
c) to encrypt the data
d) to make new ciphers

Answer: a
Clarification: Cryptanalysis is a field of study in which a cryptographic scheme is intentionally tried to breach in order to find flaws and insecurities. It is used to make sure that the scheme is least vulnerable to attacks.

7. Which one of the following is a cryptographic protocol used to secure HTTP connection?
a) stream control transmission protocol (SCTP)
b) transport layer security (TLS)
c) explicit congestion notification (ECN)
d) resource reservation protocol

Answer: b
Clarification: TLS has strong message authentication and key-material generation to prevent eavesdropping, tampering and message forgery. It has been used since the year 1996.

8. Voice privacy in GSM cellular telephone protocol is provided by _______
a) A5/2 cipher
b) b5/4 cipher
c) b5/6 cipher
d) b5/8 cipher

Answer: a
Clarification: The A5/2 cipher was published in the year 1996 and was cryptanalysed in the same year within a month. It’s use was discontinued from the year 2006 as it was really weak.

9. ElGamal encryption system is __________
a) symmetric key encryption algorithm
b) asymmetric key encryption algorithm
c) not an encryption algorithm
d) block cipher method

Answer: b
Clarification: The ELGamal encryption system was made by Taher Elgamal in the year 1985 and is an asymmetric key algorithm. It is popularly used in PGP and other systems.

10. Cryptographic hash function takes an arbitrary block of data and returns _________
a) fixed size bit string
b) variable size bit string
c) both fixed size bit string and variable size bit string
d) variable sized byte string

Answer: a
Clarification: Cryptographic hash functions are used in digital signatures and message authentication codes. The only issue with it is that it returns the same hash value every time for a message making it vulnerable to attackers to evaluate and break the cipher.

Computer Networks Multiple Choice Questions on “Network Layer”.

1. The network layer is concerned with __________ of data.
a) bits
b) frames
c) packets
d) bytes

Answer: c
Clarification: In computer networks, the data from the application layer is sent to the transport layer and is converted to segments. These segments are then transferred to the network layer and these are called packets. These packets are then sent to data link layer where they are encapsulated into frames. These frames are then transferred to physical layer where the frames are converted to bits.

2. Which one of the following is not a function of network layer?
a) routing
b) inter-networking
c) congestion control
d) error control

Answer: d
Clarification: In the OSI model, network layer is the third layer and it provides data routing paths for network communications. Error control is a function of the data link layer and the transport layer.

3. A 4 byte IP address consists of __________
a) only network address
b) only host address
c) network address & host address
d) network address & MAC address

Answer: c
Clarification: An ip address which is 32 bits long, that means it is of 4 bytes and is composed of a network and host portion and it depends on address class. The size of the host address and network address depends upon the class of the address in classful IP addressing.

4. In virtual circuit network each packet contains ___________
a) full source and destination address
b) a short VC number
c) only source address
d) only destination address

Answer: b
Clarification: A short VC number also called as VCID (virtual circuit identifier) is a type of identifier which is used to distinguish between several virtual circuits in a connection oriented circuit switched network. Each virtual circuit is used to transfer data over a larger packet switched network.

5. Which of the following routing algorithms can be used for network layer design?
a) shortest path algorithm
b) distance vector routing
c) link state routing
d) all of the mentioned

Answer: d
Clarification: The routing algorithm is what decides where a packet should go next. There are several routing techniques like shortest path algorithm, static and dynamic routing, decentralized routing, distance vector routing, link state routing, Hierarchical routing etc. The routing algorithms go hand in hand with the operations of all the routers in the networks. The routers are the main participants in these algorithms.

6. Which of the following is not correct in relation to multi-destination routing?
a) is same as broadcast routing
b) contains the list of all destinations
c) data is not sent by packets
d) there are multiple receivers

Answer: c
Clarification: In multi-destination routing, there is more than one receiver and the route for each destination which is contained in a list of destinations is to be found by the routing algorithm. Multi-destination routing is also used in broadcasting.

7. A subset of a network that includes all the routers but contains no loops is called ________
a) spanning tree
b) spider structure
c) spider tree
d) special tree

Answer: a
Clarification: Spanning tree protocol (STP) is a network protocol that creates a loop free logical topology for ethernet networks. It is a layer 2 protocol that runs on bridges and switches. The main purpose of STP is to ensure that you do not create loops when you have redundant paths in your network.

8. Which one of the following algorithm is not used for congestion control?
a) traffic aware routing
b) admission control
c) load shedding
d) routing information protocol

Answer: d
Clarification: The Routing Information Protocol (RIP) is used by the network layer for the function of dynamic routing. Congestion control on the flow of the traffic in the network and uses algorithms like traffic aware routing, admission control and load shedding to deal with congestion.

9. The network layer protocol for internet is __________
a) ethernet
b) internet protocol
c) hypertext transfer protocol
d) file transfer protocol

Answer: b
Clarification: There are several protocols used in Network layer. Some of them are IP, ICMP, CLNP, ARP, IPX, HRSP etc. Hypertext transfer protocol is for application layer and ethernet protocol is for data link layer.

10. ICMP is primarily used for __________
a) error and diagnostic functions
b) addressing
c) forwarding
d) routing

Answer: a
Clarification: ICMP abbreviation for Internet Control Message Protocol is used by networking devices to send error messages and operational information indicating a host or router cannot be reached. ICMP operates over the IP packet to provide error reporting functionality as IP by itself cannot report errors.