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TCP/IP Questions and Answers

51.

Which protocol is used to send emails ?

Exam Year(s)

Tripura Public Service Commission - 2026,

Answer: C

Emails are sent with SMTP.

The Simple Mail Transfer Protocol carries outgoing mail from the sender's mail client to a mail server and between mail servers, normally on port 25 or 587.

POP3 is the near miss: it is used to retrieve, not send, mail from a server, as is IMAP. FTP transfers files and HTTP transfers web pages.

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52.

Both hosts and routers are TCP/IP protocol software. However, routers do not use protocol from all layers. The layer for which protocol software is not needed by a router is

Exam Year(s)

UGC NET - 2012,

Answer: A

A router does not need software for Layer 5, the Application layer.

A router moves packets between networks. It needs the physical layer to send and receive bits, the network interface layer to frame them, and the internet layer (IP) to route them. It does not need the transport or application layer protocols, because it does not deal with the end-to-end conversation or the applications such as mail or file transfer, which run only in the hosts. So options (B), (C) and (D) are layers a router does need.

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53.

Which of the following IP address class is a multicast address ?

Exam Year(s)

UGC NET - 2012,

Answer: D

The IPv4 address classes are fixed by the leading bits of the first octet: class A begins with 0, class B with 10, class C with 110, class D with 1110 and class E with 1111. Class D addresses, from 224 to 239 in the first octet, are reserved for multicast, where a datagram is delivered to every member of a group. Classes A, B and C carry unicast addresses for single hosts. The answer is Class D, option (D).

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54.

Which layer of OSI reference model uses the ICMP (Internet Control Message Protocol) ?

Exam Year(s)

UGC NET - 2012,

Answer: C

ICMP, the Internet Control Message Protocol, carries error and control messages about IP datagrams, such as destination unreachable or the echo request used by ping, and it works with IP, so it belongs to the network layer of the OSI reference model. The transport layer has TCP and UDP, the data link layer works with frames on a link, and the application layer holds protocols like HTTP. The answer is Network layer, option (C).

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55.

What is the size (in terms of bits) of Header length field in IPV4 header ?

Exam Year(s)

UGC NET - 2012,

Answer: B

The header length field in the IPv4 header, IHL, is 4 bits wide. It gives the length of the header in units of 32-bit words, so its largest value of 15 gives a header of at most 60 bytes, and its smallest value is 5, for the 20-byte header without options. Because the field is only 4 bits, the header cannot be longer than 60 bytes. The other sizes, 2, 8 and 16 bits, are not the width of that field. The answer is 4, option (B).

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56.

Which of the following addresses is used to deliver a message to the correct application program running on a host ?

Exam Year(s)

UGC NET - 2013,

Answer: A

The address that delivers a message to the right application program on a host is the port address, option (A). The IP (logical) address identifies the host on the network, and the physical (MAC) address identifies the interface on a local link, but both stop at the machine. Once the packet has reached the host, the transport layer uses the port number in the TCP or UDP header to hand the data to the process that is listening on that port, such as 80 for a web server. So (B) IP, (C) logical and (D) physical addresses are wrong, since they find a host or an interface and not an application.

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57.

In IPv4 header, the ______ field is needed to allow the destination host to determine which datagram a newly arrived fragments belongs to.

Exam Year(s)

UGC NET - 2013,

Answer: A

The identification field of the IPv4 header lets the destination host decide which datagram a newly arrived fragment belongs to, option (A). The sender gives every datagram a number in this field and every fragment copies it, so fragments of the same datagram can be gathered together even when they arrive mixed with fragments of others. The fragment offset field tells where the fragment fits in the original datagram, so it orders the pieces but does not say which datagram they belong to. Time to live limits the hops a datagram may take, and the header checksum only checks the header for errors, so (B), (C) and (D) are wrong.

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58.

Which of the following field of the TCP header tells how many bytes may be sent starting at the byte acknowledged ?

Exam Year(s)

UGC NET - 2013,

Answer: B

The window size field of the TCP header tells how many bytes may be sent starting at the byte acknowledged. It is the receiver's advertised window and is used for flow control.

The TCP header length field gives the size of the header in words. The acknowledgement number is the number of the next byte expected. The urgent pointer shows the position of urgent data in the segment. None of these says how many bytes may be sent, so the window size is the answer.

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59.

Match the following :

(a) UDP(i) Message Transfer Protocol
(b) OSPF(ii) Bit-oriented Protocol
(c) SMTP(iii) Interior Gateway Routing Protocol
(d) HDLC(iv) Connectionless Transport Protocol

Codes :
(a) (b) (c) (d)

Exam Year(s)

UGC NET - 2013,

Answer: C

The correct matches are UDP with the connectionless transport protocol, OSPF with the interior gateway routing protocol, SMTP with the message transfer protocol and HDLC with the bit-oriented protocol. This is the code (iv) (iii) (i) (ii).

UDP provides connectionless transport, OSPF is a link-state routing protocol used inside an autonomous system, SMTP transfers mail messages, and HDLC is a bit-oriented data link protocol. The other codes give SMTP or HDLC to the wrong description, or UDP to the routing protocol, and are wrong.

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60.

Which of the following is used in the options field of IPv4 ?

Exam Year(s)

UGC NET - 2014,

Answer: D

The IPv4 options field is used for strict source routing, loose source routing and time stamp.

The options field carries optional features such as security, record route, strict and loose source routing and time stamp.

Since all three named options are carried in that field, choosing only one of them is incomplete. The options field of an IPv4 header can be up to 40 bytes and is rarely used. Strict source routing gives the exact path, loose source routing gives some routers that must be visited, and the time stamp option makes each router record the time. All three are legitimate uses.

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