UGC NET Computer Science Questions Set 2 | computer networks | IP addressing

Question 1

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1. An organization has a Class B Network and need to form subnet for 64 departments
what would be the appropriate Subnet Mask

1. 1. 255.255.0.0
2. 2. 255.255.64.0
3. 3. 255.255.128.0
4. 4. 255.255.252.0

Explanation Question 1
In class B network, 16 bits are used for Network ID and 16 bits are for Host ID part. In subnetting the bits are borrowed from Host portion.

Here, we want 64 subnets. so, we have to borrow 6 bits from host id part because 2⁶ = 64 number of subnets we require. Subnet mask will have total 16 + 6 bits as continuous 1's. in network id and subnet id part.

Binary form of subnet mask is : 11111111.11111111.11111100.00000000
Decimal form of subnet mask is : 255.255.252.0

So, option (4) is the correct answer.

Question 2

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2. Consider a class A, Class B and Class C network.
Consider the given IP address and subnet mask
IP Address : 150.157.100.70
Subnet Mask : 255.255.224.0
What is the address of the network in which host belong to

1. 1. 150.157.96.70
2. 2. 150.157.96.0
3. 3. 150.157.48.0
4. 4. None

Explanation Question 2

If any given IP address performs bit wise AND operation with the subnet mask, then you get the network id of the subnet to which the given IP belongs.

If IP address = 150.157.100.70 (convert it into binary form)
Binary form of IP address is : 10010110.10011101.01100100.01000110

IP address	= 10010110.10011101.01100100.01000110
Subnet mask	= 11111111. 11111111. 11100000.00000000
Bit Wise AND	= 10010110.10011101.01100000.00000000

Binary form of network address is : 10010110.10011101.01100000.00000000
Deciaml form of network address is : 150.157.96.0
Therefore, Nid = 150.157.96.0

So, option (2) is the correct answer.

Question 3

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3. Subnet mask for a particular network is 255.255.31.0 then tell about Which pairs of IP addresses could belong to this network ?

1. 1. 172.57.88.62 and 172.56.87.23.2
2. 2. 10.35.28.2 and 10.35.29.4
3. 3. 191.203.31.87 and 191.234.31.88
4. 4. 128.8.129.43 and 128.8.161.55

Explanation Question 3

If IP₁ and IP₂ belongs to same network, we must have
IP₁ BITWISE-AND "Subnet mask" = Network Address
= IP₂ BITWISE-AND "Subnet mask"

Out of the 4 options, only option D matches.
128.8.129.43 BITWISE-AND 255.255.31.0 = 128.8.1.0
128.8.161.55 BITWISE-AND 255.255.31.0 = 128.8.1.0

Both addresses belongs to same network.
You can check rest of the options.

Question 4

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4. If a class B IP address has the subnet mask 255.255.248.0 then How many maximum host will be possible in the network?

1. 1. 1022
2. 2. 1023
3. 3. 2046
4. 4. 2047

Explanation Question 4

Binary form of subnet mask of 255.255.248.0 is : 11111111.11111111.11111000.00000000 From above binary form of subnet mask. you can say that subnet mask of 255.255.248.0 will have a 21 bits network id and having 11 host bits.

Given the subnet mask, you can calculate the number of hosts using the formula below:
2^h - 2, where h is the number of host bits (in simple terms the number of zeros in the subnet mask)

This network will have total 2048 (2¹¹ ) hosts. The first address is the network address, while the last one is the broadcast ip address, thus we subtract 2 addresses, then there can be a maximum 2046 hosts.

So, option (3) is the correct answer.

Question 5

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5. If a Class B IP address is split into subnet and 6 bits are used for subnet. What is maximum number of subnet and hosts per subnet ?

1. 1. 62 subnets and 262142 hosts
2. 2. 64 subnets and 262142 hosts
3. 3. 62 subnets and 1022 hosts
4. 4. 64 subnets and 1024 hosts

Explanation Question 5

3

Question 6

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6. Consider the IP address 25.193.155.233. How many bits are there in Network Id and Host Id ?

1. 1. 24 bit for NID, 8 bits for HID
2. 2. 8 bit for NID, 24 bits for HID
3. 3. 16 bit for NID, 16 bits for HID
4. 4. none

Explanation Question 6

2

Question 7

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7. Find the wrong statement among the following related to Subnetting?

1. 1. It can be applied only for single network
2. 2. It is used to improve security
3. 3. Here, bits are borrowed from network ID portion
4. 4. Here, bits are borrowed from host ID portion

Explanation Question 7

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Question 8

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8. Logical addressing system is used by which device ?

1. 1. Hub
2. 2. Switch
3. 3. bridge
4. 4. Router

Explanation Question 8

4

Question 9

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9. Which of the following is not true about Supernetting?

1. 1. It is used to increase security
2. 2. It is applicable for two or more networks
3. 3. Bits are borrowed from network ID portion
4. 4. It is used to improve flexibility of IP address allotment

Explanation Question 9

1

Question 10

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10. What is the network ID of the IP address 225.100.123.71?

1. 1. 225.100.123.70
2. 2. 225.100.123.72
3. 3. 225.100.123.75
4. 4. It does not has any network ID

Explanation Question 10

4

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UGC NET computer networks questions set 1 | Internet Protocols

Question 1

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1. The protocol data unit(PDU) for the application layer in the Internet stack is

1. 1. Segment
2. 2. Datagram
3. 3. Message
4. 4. Frame

Explanation Question 1

• For Application, Presentation and Session layers, the PDU is message
• For Transport layer, PDU is segment for TCP and datagram for UDP
• For Network layer, PDU is packet
• For Datalink layer, PDU is frames
• For physical layer, PDU is stream of bits

The Protocol Data Unit for Application layer in the Internet Stack (or TCP/IP) is called Message.

Option 3 is correct answer

Question 2

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2. Which of the following transport layer protocols is used to support electronic mail?

1. 1. SMTP
2. 2. IP
3. 3. TCP
4. 4. UDP

Explanation Question 2

There are three primary TCP/IP protocols for E-Mail management:

• Post Office Protocol (POP)
• Simple Mail Transfer Protocol (SMTP)
• Internet Message Access Protocol (IMAP)

They all are Application Layer Protocols

Once a client connects to the E-mail Server, there may be 0(zero) or more SMTP transactions. If the client has no mail to send, then there are no SMTP transactions. Every e-mail message sent is an SMTP transfer.

SMTP is only used to send (push) messages to the server.
POP and IMAP are used to receive messages as well as manage the mailbox contents(which includes tasks such as deleting, moving messages etc.).

E-mail uses SMTP as application layer protocol. TCP and UDP are two transport layer protocols. SMTP uses TCP as transport layer protocol as TCP is reliable.

Option 3 is correct answer

Question 3

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3. In the IPv4 addressing format, the number of networks allowed under Class C addresses is

1. 1. 2¹⁴
2. 2. 2⁷
3. 3. 2²¹
4. 4. 2²⁴

Explanation Question 3

We have total 32 bits in the IPV4 network

• Class A = 8 network bits + 24 Host bits
• Class B = 16 network bits + 16 Host bits
• Class C = 24 network bits + 8 host bits
• Class D (multicast)

For class C address, size of network field is 24 bits. But first 3 bits reserved for the network id. So, first 3 bits are fixed as 110; hence total number of networks possible is 2²¹.

Option 3 is correct answer

Reference : IPv4 addressing - Classful addressing

Question 4

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4. A layer-4 firewall ( a device that can look at all protocol headers up to the transport layer) CANNOT

1. 1. block HTTP traffic during 9:00PM and 5:00AM
2. 2. block all ICMP traffic
3. 3. stop incoming traffic from a specific IP address but allow outgoing traffic to same IP
4. 4. block TCP traffic from a specific user on a specific IP address on multi-user system during 9:00PM and 5:00AM

Answer 1

Option 1 is correct answer

Question 5

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5. Packets of the same session may be routed through different paths in:

1. 1. TCP, but not UDP
2. 2. TCP and UDP
3. 3. UDP, but not TCP
4. 4. Neither TCP nor UDP

Explanation Question 5

Routing happens in Network layer and hence has no dependency with the the transport layer protocols TCP and UDP. The transport layer protocol- whether TCP or UDP is hidden to the router and the routing path is determined based on the the network configuration at the time and hence can change even during a session. Packets of same session may be routed through different routes. Most networks don’t use static routing, but use some form of adaptive routing where the paths used to route two packets for same session may be different due to congestion on some link, or some other reason.

So, option 2 is correct answer

Reference 1 : Connection-Oriented and Connectionless Protocols

Reference 2 : If TCP is connection oriented why do packets follow different paths?

Question 6

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6. The address resolution protocol (ARP) is used for:

1. 1. Finding the IP address from the DNS
2. 2. Finding the IP address of the default gateway
3. 3. Finding the IP address that corresponds to a MAC address
4. 4. Finding the MAC address that corresponds to an IP address

Explanation Question 6

Address Resolution Protocol (ARP) is a request and reply protocol used to find MAC address from IP address.

When a packet is send to the data link layer from network layer IP address & MAC address of of the sender and the gateway of the network is attached. The MAC address of the gateway is not known to the sender. So, ARP (Address Resolution Protocol) request is generated with the IP address of the gateway and is broadcasted, gateway sends reply with it’s MAC address and every other PC/Router except the gateway discards this ARP request. So, ARP Protocol is used in finding the MAC address that corresponds to an IP address.

So, option 4 is correct answer

Reference : ARP (Address Resolution Protocol) explained

Question 7

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7. Which one of the following uses UDP as the transport protocol?

1. 1. HTTP
2. 2. Telnet
3. 3. DNS
4. 4. SMTP

Explanation Question 7

Find a list of popular Internet applications and their underlying transport and application layer Protocols.

Application	Application Layer Protocol	Underlying Transport layer protocol
Electronic Mail	SMTP	TCP
Remote Terminal access	Telnet	TCP
Web	HTTP	TCP
Name Translation	DNS	Typically UDP
File Transfer	FTP	TCP
Network Management	SNMP	Typically UDP
Routing Protocol	RIP	Typically UDP

UDP is a stateless, connection-less and unreliable protocol.

• HTTP needs connection to be established and thus, uses TCP.
• Telnet is a byte stream protocol which again needs connection establishment ,thus uses TCP.
• DNS needs request and response ,it needs a protocol in which a server can answer the small queries of large number of users. As UDP is fast and stateless it is the most suitable protocol and thus,it is used in DNS querying. DNS primarily uses User Datagram Protocol (UDP) on port number 53 to serve requests. DNS queries consist of a single UDP request from the client followed by a single UDP reply from the server.
• SMTP needs reliability and thus,uses TCP.

DNS uses UDP protocol whereas HTTP, Telnet and SMTP uses TCP.

So, option 3 is correct answer

Question 8

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8. Match the following:

(P) SMTP	(1) Application layer
(Q) BGP	(2) Transport layer
(R) TCP	(3) Data link layer
(S) PPP	(4) Network layer
	(5) Physical layer

1. 1. (A) P - 2  Q - 1  R - 3  S - 5
2. 2. (B) P - 1  Q - 4  R - 2  S - 3
3. 3. (C) P - 1  Q - 4  R - 2  S - 5
4. 4. (D) P - 2  Q - 4  R - 1  S - 3

Explanation Question 8

• SMTP is an application layer protocol used for e-mail transmission. SMTP servers commonly use the Transmission Control Protocol on port number 25. 
• TCP is a core transport layer protocol. Major internet applications such as the World Wide Web, email, remote administration, and file transfer rely on TCP, which is part of the Transport Layer of the TCP/IP suite.
• BGP is a network layer protocol backing the core routing decisions on the Internet. Border Gateway Protocol (BGP) is a standardized exterior gateway protocol designed to exchange routing and reachability information among autonomous systems (AS) on the Internet.
• PPP is a data link layer protocol commonly used in establishing a direct connection between two networking nodes. PPP is commonly used as a data link layer protocol for connection over synchronous and asynchronous circuits, 

So, option 2 is correct answer

Question 9

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9. Find the false statement about HTTP

1. 1. HTTP run over TCP
2. 2. HTTP allows information to be stored in url
3. 3. HTTP describe the structure of web page
4. 4. HTTP can be used to test the validity of hyper link test

Explanation Question 9

HTTP is the set of rules for transferring files (text, graphic images, sound, video, and other multimedia files) on the World Wide Web. HTTP is a transfer protocol that is used to transfer hypertext requests and information between servers and browsers.

HTTP Protocol does not describe the structure of a web page.
HTML describes the structure of a web-page.

Question 10

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10. Here some activities related to email is given
FInd the correct match for the protocol used in appropriate activity
A1: send an email from a mail client to mail server
A2:download an email in mailbox from mail server to mail client
A3: checking mail in browser

1. 1. A1 : HTTP, A2 : SMTP, A3 : POP
2. 2. A1 : SMTP, A2 : FTP , A3 : HTTP
3. 3. A1 : SMTP , A2 : POP, A3 : HTTP
4. 4. A1 : POP, A2 : SMTP, IA3 : ICMP

Explanation Question 10

• Client mail box to server → HTTP and SMTP( push protocol)
• Download mail box from server → POP and IMAP (Pull protocol)
• Check mail in Browser → HTTP

So, option 3 is correct answer

UGC NET Computer Science December 2019 | Question 1

Question 1

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Which of the learning outcomes are intended in teaching organized at understanding level?

1. 1. Longer recall and retention of facts
2. 2. Seeking of relationships and patterns among facts
3. 3. Creative construction and critical interpretation of ideas
4. 4. Mastery of facts and information

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UGC NET Computer Science December 2019 | Question 145

Question 145

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A flow graph F with entry node (1) and exit node (11) is shown below:

How many predicate nodes are there and what are their names?

1. 1. Three : (1, (2, 3), 6)
2. 2. Three: (1, 4, 6)
3. 3. Four : ((2, 3), 6, 10, 11)
4. 4. Four: ((2, 3), 6, 9, 10)

Answer : 1. Three : (1, (2, 3), 6)

Explanation Question 145

Predicate is a node that contains condition. It means at least 2 outgoing edges required to qualify as a predicate.
Total number of predicates are THREE.

1. The vertex 1 is contains 2 outgoing edges are (2,3) and 11
2. The vertex (2,3) contains 2 outgoing edges are 6 and (4,5)
3. The vertex 6 contains 2 outgoing edges are 7 and 8.

So, option 1 is correct answer

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UGC NET CS December 2019 - Question 144	UGC NET CS December 2019 - Question 146

UGC NET Computer Science December 2019 | Question 122

Question 122

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Which of the following are legal statements in C programming language?
(a) int * P= &44 ;
(b) int * P= &r ;
(c) int P= &a ;
(d) int P= a ;
Choose the correct option :

1. 1. (a) and (b)
2. 2. (b) and (c)
3. 3. (b) and (d)
4. 4. (a) and (d)

Answer : 3. (b) and (d)

Explanation Question 122

Legal Statements:

• int *P = &r;     Here, Pointer variable P is storing address of variable r.
• int P = a;          Here, P will hold value assigned by a.

Illegal Statements:

• int *P = &44;     Here, Pointer variable is storing address of number. This is not legal statement. First its needed to assign the value 44 in some variable and then address of that variable can stored by Pointer variable P.   
• int P = &a;    Here, P variable trying to store the address of the variable. It's illegal. It should be pointer in place of the int P variable.

So, option 3 is correct answer

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UGC NET CS December 2019 - Question 121	UGC NET CS December 2019 - Question 123

UGC NET Computer Science December 2019 | Question 142

Question 142

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A flow graph F with entry node (1) and exit node (11) is shown below:

What is the cyclomatic complexity of flowgraph F?

1. 1. 2
2. 2. 3
3. 3. 4
4. 4. 3

Answer : 3. 4

Explanation Question 142

To find cyclomatic complexity we have 3 formulas

1. The number of regions(R) corresponds to the cyclomatic complexity. Total number of regions(R) are 4.
2. V(G), Flow graph is defined as V(G) = P + 1 where p is the number of predicate nodes contained in the flow graph G. Predicates are 3 + 1 = 4
3. V(G), Flow graph is defined as V(G) = E - N + 2 where E is the number of flow graph edges, and N is the number of flow graph nodes.
   Edges(E) - Nodes(N) + 2
   = 11 - 9 + 2
   = 2 + 2
   = 4

So, option 3 is correct answer

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UGC NET CS December 2019 - Question 141	UGC NET CS December 2019 - Question 143

UGC NET Computer Science December 2019 | Question 141

Question 141

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A flow graph F with entry node (1) and exit node (11) is shown below:

Add caption

How many nodes are there in flowgraph F?

1. 1. 9
2. 2. 10
3. 3. 11
4. 4. 12

Answer : 1. 9

Explanation Question 141

Above graph contains 9 nodes and 11 edges.
The nodes are nothing but vertices.
Here, In above given diagram the number of rounds are the nodes
The nodes are 1, (2,3), (4,5), 6, 7, 8, 9, 10, 11.
Count of total nodes in flowgraph F are 9.

So, option 1 is correct answer

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UGC NET CS December 2019 - Question 140	UGC NET CS December 2019 - Question 142

UGC NET Computer Science December 2019 | Question 133

Question 133

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According to the ISO-9126 Standard Quality Model. match the attributes given in List-I with their definitions in List-II :

List I	List II
a. Functionality	i. Relationship between level of performance and amount of resources
b. Reliability	ii. Characteristics related with achievement of purpose
c. Efficiency	iii. Effort needed to make for improvement
d. Maintainability	iv. Capability of software to maintain

Choose the correct option from the ones given below :

1. 1. (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)
2. 2. (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)
3. 3. (a)-(ii), (b)-(iv), (c)-(i), (d)-(iii)
4. 4. (a)-(i), (b)-(ii), (c)-(iv), (d)-(iii)

Answer : 3. (a)-(ii), (b)-(iv), (c)-(i), (d)-(iii)

Explanation Question 133

6 main quality characteristics for ISO-9126 Standard Quality Model:

1. Functionality→ Characteristics related with achievement of purpose
2. Reliability → Capability of software to maintain performance of software
3. Efficiency → Relationship between level of performance and amount of resources
4. Maintainability → Effort needed to make for improvement
5. Usability → Usability only exists with regard to functionality and refers to the ease of use for a given function.
6. Portability → This characteristic refers to how well the software can adapt to changes in its environment or with its requirements.

Reference : ISO/IEC 9126

So, option 3 is correct answer

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UGC NET CS December 2019 - Question 132	UGC NET CS December 2019 - Question 134

UGC NET Computer Science December 2019 | Question 143

Question 143

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A flow graph F with entry node (1) and exit node (11) is shown below:

How many regions are there in flowgraph F?

1. 1. 2
2. 2. 3
3. 3. 4
4. 4. 8

Answer :

Explanation Question 143

The region is nothing but a combination of closed region and outer region. Any graph must have one outer region.
Here, 3 closed regions are available and one outer region is available.

• Closed 3 regions are:

1. Closed region by nodes → 1, (2, 3), (4, 5) and 10
2. Closed region by nodes → 6, 7, 8, 9
3. Closed region by nodes → (2, 3), 6, 7, 8, 9, 10 and (4, 5)

• One outer region.

So, the total number of regions are 4.

So, option 3 is correct answer

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UGC NET CS December 2019 - Question 142	UGC NET CS December 2019 - Question 144