Networking Basics Questions and Answers

Q: Four bits are used for packed sequence numbering in a sliding window protocol used in a computer network. What is the maximum window size ?

The maximum window size is 15.With 4 bits, sequence numbers run from 0 to 15, 16 in all. For a go-back-N sliding window the largest window is \(2^{4} - 1 = 15\), so that new frames cannot be confused with old ones.A window of 16 would make sequence numbers ambiguous, and 4 and 8 are smaller than the allowed maximum (8 applies to selective repeat). The sequence numbers modulo 16 can distinguish 15 outstanding frames from each other and from a retransmission, so a window larger than 15 would let the receiver accept an old frame as a new one.

Q: How often are BPDUs sent from a layer 2 device?

Correct answer: Every 2 secondsBridge protocol data units are sent every two seconds by default, which is the spanning tree hello time. They carry the bridge ID and path cost information from which every switch determines the root bridge, its own root port and any blocking ports. The interval matters because convergence times are derived from it: max age is twenty seconds, ten missed hellos, and forward delay fifteen.

Q: How many broadcast domains are created when you segment a network with a 12-port switch?

Correct answer: 1A switch breaks up collision domains, not broadcast domains: a broadcast frame arriving on one port is flooded out of all the others, so all twelve ports remain in a single broadcast domain by default. Splitting that domain requires either a router or VLANs configured on the switch, each VLAN forming a broadcast domain of its own. The complementary question - how many collision domains - gives twelve.

Q: In a network with dozens of switches, how many root bridges would you have?

Correct answer: 1Spanning tree elects exactly one root bridge per broadcast domain, however many switches there are, and every other switch computes its shortest path to that root. The election is by lowest bridge ID - priority first, then MAC address as the tiebreaker - which is why the priority is normally set deliberately on the switch that should win, rather than left to the accident of which switch has the lowest MAC address.

Q: Which protocol does DHCP use at the Transport layer?

Correct answer: UDPDHCP runs over UDP, on port 67 for the server and 68 for the client. It must, because the client has no IP address when it begins: the initial DHCPDISCOVER is a broadcast from 0.0.0.0, and TCP cannot establish a connection without addresses at both ends. IP is a network layer protocol rather than a transport one, and ARP is a layer 2 resolution protocol.

Q: In which transmission mode can data travel in both directions, but only one direction at a time ?

Correct answer: Half-duplexHalf-duplex allows each end to transmit in turn but never simultaneously, as with a walkie-talkie. Simplex permits one direction only, and full-duplex allows both ends to send at once, as an ordinary telephone call does.

121.

Which layers of the OSI reference model are host-to-host layers ?

A.Transport, Session, Presentation, Application
B.Network, Transport, Session, Presentation
C.Data-link, Network, Transport, Session
D.Physical, Data-link, Network, Transport

Exam Year(s)

UGC NET - 2014,

Answer: A

The host-to-host layers are transport, session, presentation and application.

In the grouping used in the key, the lower layers handle the network between adjacent nodes, and the upper four layers work end to end between the two hosts.

The other options include the physical, data-link or network layer, which are node to node or network layers. Layers 5 to 7 and the transport layer work between the end systems, while layers 1 to 3 work hop by hop through the network, so they are not host-to-host layers. This is the distinction the question rests on.

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122.

Four bits are used for packed sequence numbering in a sliding window protocol used in a computer network. What is the maximum window size ?

A.4
B.8
C.15
D.16

Exam Year(s)

UGC NET - 2014,

Answer: C

The maximum window size is 15.

With 4 bits, sequence numbers run from 0 to 15, 16 in all. For a go-back-N sliding window the largest window is \(2^{4} - 1 = 15\), so that new frames cannot be confused with old ones.

A window of 16 would make sequence numbers ambiguous, and 4 and 8 are smaller than the allowed maximum (8 applies to selective repeat). The sequence numbers modulo 16 can distinguish 15 outstanding frames from each other and from a retransmission, so a window larger than 15 would let the receiver accept an old frame as a new one.

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123.

How often are BPDUs sent from a layer 2 device?

A.Never
B.Every 2 seconds
C.Every 10 minutes
D.Every 30 seconds

Answer: B

Correct answer: Every 2 seconds

Bridge protocol data units are sent every two seconds by default, which is the spanning tree hello time. They carry the bridge ID and path cost information from which every switch determines the root bridge, its own root port and any blocking ports. The interval matters because convergence times are derived from it: max age is twenty seconds, ten missed hellos, and forward delay fifteen.

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124.

How many broadcast domains are created when you segment a network with a 12-port switch?

A.1
B.2
C.5
D.12

Answer: A

Correct answer: 1

A switch breaks up collision domains, not broadcast domains: a broadcast frame arriving on one port is flooded out of all the others, so all twelve ports remain in a single broadcast domain by default. Splitting that domain requires either a router or VLANs configured on the switch, each VLAN forming a broadcast domain of its own. The complementary question - how many collision domains - gives twelve.

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125.

In a network with dozens of switches, how many root bridges would you have?

A.1
B.2
C.5
D.12

Answer: A

Correct answer: 1

Spanning tree elects exactly one root bridge per broadcast domain, however many switches there are, and every other switch computes its shortest path to that root. The election is by lowest bridge ID - priority first, then MAC address as the tiebreaker - which is why the priority is normally set deliberately on the switch that should win, rather than left to the accident of which switch has the lowest MAC address.

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126.

Two devices are in network if __________

A.a process in one device is able to exchange information with a process in another device
B.a process is running on both devices
C.PIDs of the processes running of different devices are same
D.a process is active and another is inactive

Answer: A

Explanation: A computer network, or data network, is a digital telecommunications network which allows nodes to share resources. In computer networks, computing devices exchange data with each other using connections between nodes. The nodes have certain processes which enable them to share a specific type of data using a distinct protocol.

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127.

Which of the following networks extends a private network across public networks?

A.local area network
B.virtual private network
C.enterprise private network
D.storage area network

Answer: B

Explanation: A virtual private network extends a private network across a public network, and enables users to send and receive data across shared or public networks as if their computing devices were directly connected to the private network.VPN provides enhanced security and online anonymity to users on the internet. It is also used to unblock websites which are unavailable in certain regions.

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128.

Which protocol does DHCP use at the Transport layer?

A.IP
B.TCP
C.UDP
D.ARP

Answer: C

Correct answer: UDP

DHCP runs over UDP, on port 67 for the server and 68 for the client. It must, because the client has no IP address when it begins: the initial DHCPDISCOVER is a broadcast from 0.0.0.0, and TCP cannot establish a connection without addresses at both ends. IP is a network layer protocol rather than a transport one, and ARP is a layer 2 resolution protocol.

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129.

In which transmission mode can data travel in both directions, but only one direction at a time ?

A.Simplex
B.Half-duplex
C.Full-duplex
D.Multiplex

Answer: D

Correct answer: Half-duplex

Half-duplex allows each end to transmit in turn but never simultaneously, as with a walkie-talkie. Simplex permits one direction only, and full-duplex allows both ends to send at once, as an ordinary telephone call does.

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130.

A _________ set of rules that governs data communication.

A.Protocols
B.Standards
C.RFCs
D.Servers

Answer: A

Explanation: In communications, a protocol refers to a set of rules and regulations that allow a network of nodes to transmit and receive information. Each layer in the network model has a protocol set, for example, the transport layer has TCP and UDP protocols.

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