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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