Category: Computer Networks Objective Questions

Computer Networks Multiple Choice Questions on “FTP”.

1. Expansion of FTP is __________
a) Fine Transfer Protocol
b) File Transfer Protocol
c) First Transfer Protocol
d) Fast Transfer Protocol

Answer: b
Clarification: File Transfer Protocol is an application layer protocol used to share “files” between a server and a client. The protocol uses two separate ports for data and control connections: port 20 for data and port 21 for control.

2. FTP is built on _____ architecture.
a) Client-server
b) P2P
c) Data centric
d) Service oriented

Answer: a
Clarification: An FTP connection includes a Server and a Client which wish to share a number of data files. The server can transfer files with multiple clients at the same time while the client communicates with only one server at a time.

3. FTP uses _________ parallel TCP connections to transfer a file.
a) 1
b) 2
c) 3
d) 4

Answer: b
Clarification: Control connection using FTP port: 21, and data connection using FTP port: 20. The FTP session is started or ended using port 21 and the actual data i.e. files are sent through port 20.

4. Identify the incorrect statement regarding FTP.
a) FTP stands for File Transfer Protocol
b) FTP uses two parallel TCP connections
c) FTP sends its control information in-band
d) FTP sends exactly one file over the data connection

Answer: c
Clarification: FTP is out-of-band because the data connection is done separately through port 20 and control connection is done separately through port 21.

5. If 5 files are transferred from server A to client B in the same session. The number of TCP connections between A and B is _______
a) 5
b) 10
c) 2
d) 6

Answer: d
Clarification: The client would first initiate the TCP control connection through port 21. Then for every file transfer, a separate connection would be made through port 20. Now, since we have five files to be transferred, 1 control connection + 5 data connections = 6 total TCP connections.

6. FTP server _____________
a) Maintains state information
b) Is stateless
c) Has single TCP connection for a file transfer
d) Has UDP connection for file transfer

Answer: a
Clarification: FTP server maintains state information of every control connection to keep track of the active and inactive connections in the session. This helps the server decide which connection to terminate, in case the connection is inactive for too long.

7. The commands, from client to server, and replies, from server to client, are sent across the control connection in ________ bit ASCII format.
a) 8
b) 7
c) 3
d) 5

Answer: b
Clarification: FTP was designed to transmit commands only in English characters that are possible with just 7 bits in ASCII. Even the media has to be converted to ASCII before transmission.

8. Find the FTP reply whose message is wrongly matched.
a) 331 – Username OK, password required
b) 425 – Can’t open data connection
c) 452 – Error writing file
d) 452 – Can’t open data connection

Answer: d
Clarification: The correct response code for the message “Can’t open data connection” is 425. Response code 452 is sent usually when the connection is suddenly closed.

9. The data transfer mode of FTP, in which all the fragmenting has to be done by TCP is ________
a) Stream mode
b) Block mode
c) Compressed mode
d) Message mode

Answer: a
Clarification: Stream mode is the default mode of FTP, in which the TCP transforms/fragments the data into segments, and then after the transmission is completed, converts it back to stream of bytes.

10. The password is sent to the server using ________ command.
a) PASSWD
b) PASS
c) PASSWORD
d) PWORD

Answer: b
Clarification: The PASS command, preceded by the username, completes the user’s identification for access control in an FTP session. Without the valid password, the user won’t be able to initiate the FTP connection.

Computer Networks Multiple Choice Questions on “Congestion Control”.

1. Two broad categories of congestion control are
a) Open-loop and Closed-loop
b) Open-control and Closed-control
c) Active control and Passive control
d) Active loop and Passive loop

Answer: a
Clarification: Open loop congestion control techniques are used to prevent congestion before it even happens by enforcing certain policies. Closed loop congestion control techniques are used to treat congestion after it has happened.

2. In open-loop control, policies are applied to __________
a) Remove after congestion occurs
b) Remove after sometime
c) Prevent before congestion occurs
d) Prevent before sending packets

Answer: c
Clarification: Open loop congestion control techniques are used to prevent congestion before it even happens by enforcing certain policies. Retransmission policy, window policy and acknowledgement policy are some policies that might be enforced.

3. Retransmission of packets must not be done when _______
a) Packet is lost
b) Packet is corrupted
c) Packet is needed
d) Packet is error-free

Answer: d
Clarification: Retransmission refers to the sender having to resend the packet to the receiver. It needs to be done only when some anomaly occurs with the packet like when the packet is lost or corrupted.

4. In Go-Back-N window, when the timer of the packet times out, several packets have to be resent even some may have arrived safe. Whereas in Selective Repeat window, the sender resends ___________
a) Packet which are not lost
b) Only those packets which are lost or corrupted
c) Packet from starting
d) All the packets

Answer: b
Clarification: In Selective Repeat, the sender side uses a searching algorithm to find the packets which need to be retransmitted based on the negative acknowledgements received and then resends only those packets thus saving bandwidth.

5. Discarding policy is mainly done by _______
a) Sender
b) Receiver
c) Router
d) Switch

Answer: c
Clarification: The discarding policy adopted by the routers mainly states that the routers discard sensitive or corrupted packets that it receives, thus controlling the integrity of the packet flow. The discarding policy is adopted as an open loop congestion control technique.

6. Closed-Loop control mechanisms try to _________
a) Remove after congestion occurs
b) Remove after sometime
c) Prevent before congestion occurs
d) Prevent before sending packets

Answer: a
Clarification: In closed loop congestion control, methods are implemented to remove congestion after it occurs. Some of the methods used are backpressure and choke packet.

7. The technique in which a congested node stops receiving data from the immediate upstream node or nodes is called as _______
a) Admission policy
b) Backpressure
c) Forward signaling
d) Backward signaling

Answer: b
Clarification: In this closed loop congestion control technique, the congested node propagates in the opposite direction of the data flow to inform the predecessor node to reduce the flow of packets. This is why this technique is called a node-to-node congestion control technique.

8. Backpressure technique can be applied only to _______
a) Congestion networks
b) Closed circuit networks
c) Open circuit networks
d) Virtual circuit networks

Answer: d
Clarification: In Virtual circuit networks, each node knows the upstream node from which a flow data is coming. So, it makes possible for the congested node to track the source of the congestion and then inform that node to reduce the flow to remove congestion.

9. The packet sent by a node to the source to inform it of congestion is called _______
a) Explicit
b) Discard
c) Choke
d) Backpressure

Answer: c
Clarification: Choke packet is sent by a node to the source to inform it of congestion. Two choke packet techniques can be used for the operation called hop-by-hop choke packet and source choke packet.

10. In the slow-start algorithm, the size of the congestion window increases __________ until it reaches a threshold.
a) exponentially
b) additively
c) multiplicatively
d) suddenly

Answer: a
Clarification: In slow-start algorithm, the size of the congestion window increases exponentially until it reaches a threshold. When it reaches the threshold, it stops increasing and continues sending packets through the threshold window thus preventing congestion.

11. In the congestion avoidance algorithm, the size of the congestion window increases ____________ until congestion is detected.
a) exponentially
b) additively
c) multiplicatively
d) suddenly

Answer: b
Clarification: In the congestion avoidance algorithm, the size of the congestion window increases additively until congestion is detected. Once congestion is detected, the size of congestion window is decreased once and then the packets are transmitted to achieve congestion avoidance.

Computer Networks Multiple Choice Questions on “RIP v1”.

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

Answer: a
Clarification: RIP v1 has network diameter is more than 17 hops. It uses classful routing and the routing updates are broadcasted over the network. It notifies routers about the update so that they update their own routing tables.

2. How often does a RIPv1 router broadcast its routing table by default?
a) Every 30 seconds
b) Every 60 seconds
c) Every 90 seconds
d) RIPv1 does not broadcast periodically

Answer: a
Clarification: RIPv1 router broadcasts its routing table every 30 seconds by default. The broadcasted routing table can be used by other routers to find the shortest path among the network devices.

3. Which command displays RIP routing updates?
a) Show IP route
b) Debug IP rip
c) Show protocols
d) Debug IP route

Answer: b
Clarification: The debug IP rip command is used to show the Internet Protocol (IP) Routing Information Protocol (RIP) updates being sent and received on the router. It verifies that the updates are being broadcasted and not multicasted.

4. Two connected routers are configured with RIP routing. What will be the result when a router receives a routing update that contains a higher-cost path to a network already in its routing table?
a) The updated information will be added to the existing routing table Debug IP rip
b) The update will be ignored and no further action will occur Debug IP route
c) The updated information will replace the existing routing table entry
d) The existing routing table entry will be deleted from the routing table and all routers will exchange routing updates to reach convergence

Answer: b
Clarification: When a routing update is received by a router, the router first checks the administrative distance (AD) and always chooses the route with the lowest AD. However, if two routes are received and they both have the same AD, then the router will choose the one route with the lowest metrics, or in RIP’s case, hop count.

5. You type debug IP rip on your router console and see that 172.16.10.0 is being advertised to you with a metric of 16. What does this mean?
a) The route is 16 hops away Debug IP rip
b) The route has a delay of 16 microseconds Debug IP route
c) The route is inaccessible
d) The route is queued at 16 messages a second

Answer: c
Clarification: You cannot have 16 hops on a RIP network by default, because the max default hops possible is 15. If you receive a route advertised with a metric of 16, this means it is inaccessible.

6. Default administrative distance of a static route is ________
a) 0
b) 90
c) 100
d) 1

Answer: d
Clarification: 1 is the default administrative distance of Static Route. 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.

7. Which protocol gives a full route table update every 30 seconds?
a) IEGRP
b) RIP
c) ICMP
d) IP

Answer: b
Clarification: RIP gives a full route table update every 30 seconds. The broadcasted routing table can be used by other routers to find the shortest path among the network devices.

8. _________ is the default administrative distance of RIP.
a) 0
b) 90
c) 120
d) 130

Answer: c
Clarification: The default administrative distance is the default count of numbers assigned to arbitrary routes to a destination. The default administrative distance of RIP is 120. It is used to find the shortest route amongst the number of paths available.

9. Which statement is true regarding classless routing protocol?
a) The use of discontinuous networks is not allowed
b) Use of variable length subnet masks is permitted
c) RIPv1 is a classless routing protocol
d) IGRP supports classes routing within the same autonomous system

Answer: b
Clarification: Use of variable length subnet masks is permitted in classless routing protocols. Also use of discontinuous networks is allowed in such routing protocols. RIPv1 is a classful routing protocol but RIPv2 is classless routing protocol.

10. Where should we use default routing?
a) On stub networks- which have only one exit path out of the network
b) Which have more than one exit path out of the network
c) Minimum five exit paths out of the network
d) Maximum five exit paths out of the network

Answer: a
Clarification: We must use default routing on stub networks. They have only one exit path out of the network, so there can be no specific path decided for such networks.

Computer Networks Multiple Choice Questions on “Physical Layer”.

1. The physical layer is concerned with ___________
a) bit-by-bit delivery
p) process to process delivery
c) application to application delivery
d) port to port delivery

Answer: a
Clarification: Physical layer deals with bit to bit delivery in networking. The data unit in the physical layer is bits. Process to process delivery or the port to port delivery is dealt in the transport layer. The various transmission mediums aid the physical layer in performing its functions.

2. Which transmission media provides the highest transmission speed in a network?
a) coaxial cable
b) twisted pair cable
c) optical fiber
d) electrical cable

Answer: c
Clarification: Fiber optics is considered to have the highest transmission speed among the all mentioned above. The fiber optics transmission runs at 1000Mb/s. It is called as 1000Base-Lx whereas IEEE standard for it is 802.3z. It is popularly used for modern day network connections due to its high transmission rate.

3. Bits can be sent over guided and unguided media as analog signal by ___________
a) digital modulation
b) amplitude modulation
c) frequency modulation
d) phase modulation

Answer: a
Clarification: In analog modulation, digital low frequency baseband signal (digital bit stream) is transmitted over a higher frequency. Whereas in digital modulation the only difference is that the base band signal is of discrete amplitude level. The bits are represented by only two frequency levels, one for high and one for low.

4. The portion of physical layer that interfaces with the media access control sublayer is called ___________
a) physical signalling sublayer
b) physical data sublayer
c) physical address sublayer
d) physical transport sublayer

Answer: a
Clarification: The portion of physical layer that interfaces with the medium access control sublayer is Physical Signaling Sublayer. The main function of this layer is character encoding, reception, decoding and performs optional isolation functions. It handles which media connection the signal should be forwarded to physically.

5. The physical layer provides __________
a) mechanical specifications of electrical connectors and cables
b) electrical specification of transmission line signal level
c) specification for IR over optical fiber
d) all of the mentioned

Answer: d
Clarification: Anything dealing with a network cable or the standards in use – including pins, connectors and the electric current used is dealt in the physical layer (Layer 1). Physical layer deals with bit to bit delivery of the data aided by the various transmission mediums.

6. In asynchronous serial communication the physical layer provides ___________
a) start and stop signalling
b) flow control
c) both start & stop signalling and flow control
d) only start signalling

Answer: c
Clarification: In asynchronous serial communication, the communication is not synchronized by clock signal. Instead of a start and stop signaling and flow control method is followed. Unlike asynchronous serial communication, in synchronous serial communication a clock signal is used for communication, so the start and stop method is not really required.

7. The physical layer is responsible for __________
a) line coding
b) channel coding
c) modulation
d) all of the mentioned

Answer: d
Clarification: The physical layer is responsible for line coding, channel coding and modulation that is needed for the transmission of the information. The physical configuration including pins, connectors and the electric current used is dealt in the physical layer based on the requirement of the network application.

8. The physical layer translates logical communication requests from the ______ into hardware specific operations.
a) data link layer
b) network layer
c) trasnport layer
d) application layer

Answer: a
Clarification: Physical layer accepts data or information from the data link layer and converts it into hardware specific operations so as to transfer the message through physical cables. Some examples of the cables used are optical fiber cables, twisted pair cables and co-axial cables.

9. A single channel is shared by multiple signals by ____________
a) analog modulation
b) digital modulation
c) multiplexing
d) phase modulation

Answer: c
Clarification: In communication and computer networks, the main goal is to share a scarce resource. This is done by multiplexing, where multiple analog or digital signals are combined into one signal over a shared medium. The multiple kinds of signals are designated by the transport layer which is the layer present on a higher level than the physical layer.

10. Wireless transmission of signals can be done via ___________
a) radio waves
b) microwaves
c) infrared
d) all of the mentioned

Answer: d
Clarification: Wireless transmission is carried out by radio waves, microwaves and IR waves. These waves range from 3 Khz to above 300 Ghz and are more suitable for wireless transmission. Radio waves can penetrate through walls and are used in radio communications, microwaves and infrared (IR) waves cannot penetrate through walls and are used for satellite communications and device communications respectively.

Computer Networks Multiple Choice Questions on “SMTP”.

1. When the mail server sends mail to other mail servers it becomes ____________
a) SMTP server
b) SMTP client
c) Peer
d) Master

Answer: b
Clarification: SMTP clients are the entities that send mails to other mail servers. The SMTP servers cannot send independent mails to other SMTP servers as an SMTP server. There are no masters or peers in SMTP as it is based on the client-server architecture.

2. If you have to send multimedia data over SMTP it has to be encoded into _______
a) Binary
b) Signal
c) ASCII
d) Hash

Answer: c
Clarification: Since only 7-bit ASCII codes are transmitted through SMTP, it is mandatory to convert binary multimedia data to 7-bit ASCII before it is sent using SMTP.

3. Expansion of SMTP is ________
b) Simple Message Transfer Protocol
c) Simple Mail Transmission Protocol
d) Simple Message Transmission Protocol

Answer: a
Clarification: SMTP or Simple Mail Transfer Protocol is an application layer protocol used to transport e-mails over the Internet. Only 7-bit ASCII codes can be sent using SMTP.

4. In SMTP, the command to write receiver’s mail address is written with the command _______
a) SEND TO
b) RCPT TO
c) MAIL TO
d) RCVR TO

Answer: b
Clarification: RCPT TO command is followed by the recipient’s mail address to specify where or to whom the mail is going to through the internet. If there is more than one receiver, the command is repeated for each address continually.

5. The underlying Transport layer protocol used by SMTP is ________
a) TCP
b) UDP
c) Either TCP or UDP
d) IMAP

Answer: a
Clarification: TCP is a reliable protocol, and Reliability is a mandatory requirement in e-mail transmission using SMTP.

6. Choose the statement which is wrong incase of SMTP?
a) It requires message to be in 7bit ASCII format
b) It is a pull protocol
c) It transfers files from one mail server to another mail server
d) SMTP is responsible for the transmission of the mail through the internet

Answer: b
Clarification: In SMTP, the sending mail server pushes the mail to receiving mail server hence it is push protocol. In a pull protocol such as HTTP, the receiver pulls the resource from the sending server.

7. Internet mail places each object in _________
a) Separate messages for each object
b) One message
c) Varies with number of objects
d) Multiple messages for each object

Answer: b
Clarification: It places all objects into one message as it wouldn’t be efficient enough if there are different messages for each object. The objects include the text and all the multimedia to be sent.

8. Typically the TCP port used by SMTP is _________
a) 25
b) 35
c) 50
d) 15

Answer: a
Clarification: The ports 15, 35 and 50 are all UDP ports and SMTP only uses TCP port 25 for reliability.

9. A session may include ________
a) Zero or more SMTP transactions
b) Exactly one SMTP transactions
c) Always more than one SMTP transactions
d) Number of SMTP transactions cant be determined

Answer: a
Clarification: An SMTP session consists of SMTP transactions only even if no transactions have been performed. But no transactions in the session might mean that the session is inactive or is just initiated.

10. Which of the following is an example of user agents for e-mail?
a) Microsoft Outlook
b) Facebook
c) Google
d) Tumblr

Answer: a
Clarification: Among the options, only Microsoft Outlook is an e-mail agent. Google is a search engine and Facebook, and Tumblr are social networking platforms. Gmail and Alpine are some other examples of e-mail agent.

11. When the sender and the receiver of an email are on different systems, we need only _________
a) One MTA
b) Two UAs
c) Two UAs and one MTA
d) Two UAs and two MTAs

Answer: d
Clarification: The sender’s User Agent (UA) submits the message to a Message Transfer Agent (MTA). Then the MTA sends the message to another MTA i.e. a mail relay. Then the receiver receives the message from the mail relay whenever it is available.

12. User agent does not support this ___________
a) Composing messages
b) Reading messages
c) Replying messages
d) Routing messages

Answer: d
Clarification: The user agent is basically a software program that allows the user to send, and receive e-mail messages. Routing of the message is done by the Message Transfer Agent.

Computer Networks Multiple Choice Questions on “Virtual Circuit”.

1. Which of the following is not a characteristic of Virtual Circuit Network?
a) There are setup and teardown phases in addition to the data transfer phase
b) Resources can be allocated during setup phase or on demand
c) All packets follow the same path established during the connection
d) Virtual circuit network is implemented in application layer

Answer: d
Clarification: Virtual circuit network is normally implemented in data link layer. It is a combination of circuit-switched network and datagram network which are implemented in the physical layer and network layer respectively.

2. The address that is unique in the scope of the network or internationally if the network is part of an international network is called as ______
a) Global address
b) Network address
c) Physical address
d) IP address

Answer: a
Clarification: Global address is a network address that is unique internationally and is used as a common address by all the users of the network. It is used to create a virtual circuit identifier.

3. The Identifier that is used for data transfer in virtual circuit network is called _______
a) Global address
b) Virtual circuit identifier
c) Network identifier
d) IP identifier

Answer: b
Clarification: A virtual circuit identifier is a type of numeric identifying address that is used to distinguish between different virtual circuits in a circuit-switched network. It is used for data transfer and has a switch scope.

4. Which of the following is not a phase of virtual circuit network?
a) Setup phase
b) Data transfer phase
c) Termination phase
d) Teardown phase

Answer: c
Clarification: There are three phases in a virtual circuit network: setup, data transfer and teardown phase. There is no termination phase in it.

5. Steps required in setup process are ___________
a) Setup request and acknowledgement
b) Setup request and setup response
c) Setup request and setup termination
d) Setup and termination steps

Answer: a
Clarification: Setup request (sent by a source) and acknowledgement (sent by the destination) are the steps in the setup process. Both the ends’ switches make table entries during the setup process.

6. During teardown phase, the source, after sending all the frames to destination, sends a _____ to notify termination.
a) teardown response
b) teardown request
c) termination request
d) termination response

Answer: b
Clarification: The source, after sending all the frames to destination sends teardown request to which, destination sends teardown response. The switches then delete the corresponding table entries.

7. Delay of the resource allocated during setup phase during data transfer is ________
a) constant
b) increases for each packet
c) same for each packet
d) different for each packet

Answer: c
Clarification: If a resource is allocated during setup phase, delay is same for each packet as there is only one-time delay during the setup phase and no delay during the data transfer phase.

8. Delay of the resource allocated on demand during data transfer is ________
a) constant
b) increases for each packet
c) same for each packet
d) different for each packet

Answer: d
Clarification: If a resource is to be allocated on demand during the data transfer phase, the delay for each packet would be different depending upon the resource requirement of the packets.

9. In virtual circuit network, the number of delay times for setup and teardown respectively are _______
a) 1 and 1
b) 1 and 2
c) 2 and 1
d) 2 and 2

Answer: a
Clarification: There is one-time delay for both setup and teardown phase. The one-time delay in setup phase is for resource allocation and the one-time delay in teardown phase is for the de-allocation of the resources.

10. In data transfer phase, how many columns does the table contain?
a) 1
b) 2
c) 3
d) 4

Answer: d
Clarification: The switch maintains a table for each Virtual Circuit Network. In the data transfer phase, it maintains 2 columns each for incoming data and outgoing data. The columns are in the following order: Source port, Source VCI, Destination port, Destination VCI.