UDP Protocol and Header MCQs: 12 Solved Questions with Explanations

UDP looks simple because its header has only four fields, but its questions test three decisions. You must know which services UDP lacks, how to decode its 8-byte header, and why an application may choose low overhead instead of built-in reliability. UDP questions range from protocol identification and hexadecimal field arithmetic to services that UDP deliberately leaves out.

1. UDP connectionless service and transport-layer role

UDP is a connectionless transport protocol: it sends datagrams without a setup handshake, built-in retransmission, flow control, or congestion control. Its smaller protocol burden can help, but UDP is not always faster on every network.

Question 1, UDP versus TCP (TPSC Assistant CEO 2024)

What is the key difference between UDP and TCP protocols in the transport layer?

A. TCP offers guaranteed delivery, while UDP is unreliable.
B. UDP is faster due to its connectionless nature.
C. TCP provides flow control and congestion control mechanisms
D. All of these.

Answer: D. All of these. TCP establishes a connection and manages reliable, ordered delivery, flow control, and congestion control. UDP omits that machinery, reducing setup and processing work, but the application and network still determine end-to-end performance.

Question 2, identifying the connectionless transport protocol (UGC NET June 2022)

Which one is a connectionless transport - layer protocol that belongs to the Internet protocol family ?

A. Transmission Control Protocol (TCP)
B. User Datagram Protocol (UDP)
C. Routing Protocol (RP)
D. Datagram Control Protocol (DCP)

Answer: B. User Datagram Protocol (UDP). UDP is the Internet family's connectionless transport-layer datagram protocol. TCP is connection-oriented; RP and DCP are distractor protocol names.

Question 3, minimal transport overhead (TPSC Assistant CEO 2024)

Which transport layer protocol is connectionless and provides minimal overhead, suitable for applications where low latency is crucial ?

A. TCP (Transmission Control Protocol)
B. UDP (User Datagram Protocol)
C. IP (Internet Protocol)
D. ICMP (Internet Control Message Protocol)

Answer: B. UDP (User Datagram Protocol). UDP uses an 8-byte header and sends without connection setup. An application can handle recovery or ordering itself; IP and ICMP are Internet-layer protocols, while TCP adds connection and reliability machinery.

2. UDP applications, broadcast use, and handshake traps

Do not memorise a rigid list of UDP applications. Ask whether fresh data matters more than retransmitting stale data, or whether the application supplies its own recovery. DNS, for example, commonly uses UDP for ordinary queries but can use TCP in defined situations.

Question 4, multimedia transport (TPSC System Analyst 2026)

Which protocol is used in the transport layer for multimedia data communication ?

A. HTTP
B. UDP
C. ICMP
D. TCP

Answer: B. UDP. The intended choice is real-time multimedia, where a fresh datagram may be more useful than a delayed retransmission. Buffering, loss concealment, or application-layer recovery may handle imperfections, but not every multimedia system uses UDP.

Question 5, application protocols carried over UDP

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

A. HTTP, DNS
B. TFTP, DNS
C. FTP, SMTP
D. TELNET, FTP

Answer: B. TFTP, DNS. TFTP is designed as a small file-transfer protocol over UDP, and DNS request-response traffic commonly uses UDP. DNS can also use TCP when required, while HTTP, FTP, SMTP, and TELNET are paired with TCP in this exam framing.

Question 6, one-way communication and connection setup

Consider the following statements, about User Datagram Protocol in transport layer,
(S1) User Datagram Protocol in transport layer Works well in unidirectional communication, suitable for broadcast information.
(S2) User Datagram Protocol in transport layer does three way handshake before sending datagrams
Which of the above is true.

A. Only S1
B. Only S2
C. Both S1 and S2
D. None of the above

Answer: A. Only S1. Connectionless datagram delivery can support one-way and broadcast-oriented communication, so S1 fits UDP. S2 is false because the three-way connection-establishment handshake is a TCP mechanism.

3. UDP header fields and hexadecimal decoding

The UDP header has four equal-width fields:

Each 16-bit field consumes four hexadecimal digits. Read each group from left to right. Their total is 16 + 16 + 16 + 16 = 64 bits = 8 bytes.

Question 7, the field absent from a UDP header

Which of the following field is not a part of UDP header?

A. Source port number
B. Destination port number
C. Window size
D. Checksum

Answer: C. Window size. A UDP header contains source port, destination port, length, and checksum. Window size belongs to TCP's flow-control design, and UDP does not carry such a field.

Question 8, decoding the source port (UGC NET June 2025)

CB84000D001C001C is the content of a UDP header in hexadecimal format. The source port number is

A. 52100
B. 13
C. 28
D. 52000

Answer: A. 52100. Split the 16 hexadecimal digits into four 16-bit words: CB84 | 000D | 001C | 001C. The source port is 0xCB84, which equals 12 x 4096 + 11 x 256 + 8 x 16 + 4 = 49152 + 2816 + 128 + 4 = 52100.

The remaining fields are 0x000D = 13 for destination port, 0x001C = 28 for UDP length, and a final 0x001C for checksum. As length covers header and data, the application data occupies 28 - 8 = 20 bytes.

4. UDP length inside an IPv4 packet

Keep three quantities separate. IPv4 Total Length includes the IP header and payload. That payload is the complete UDP datagram, whose UDP Length includes its 8-byte header and data.

Question 9, deriving UDP datagram length (HPSC 2021)

Choose the correct expression from the following for the length of UDP datagram.

A. UDP length = IP length - IP header’s length
B. UDP length = UDP length - UDP header’s length
C. UDP length = UDP length - UDP header’s length
D. UDP length = UDP length + UDP header’s length

Answer: A. UDP length = IP length - IP header’s length. An IPv4 packet carrying UDP has its IP header followed by the complete UDP datagram, so this subtraction isolates the UDP header plus data.

For IPv4 Total Length 60 bytes and IHL 5, the IP header is 5 x 4 = 20 bytes. UDP length is 60 - 20 = 40 bytes; application data is 40 - 8 = 32 bytes.

5. UDP flow control, congestion control, and retransmission

UDP provides no flow control, congestion control, retransmission, or ordered delivery. An application can add such logic above UDP without making it a UDP service.

Question 10, the false UDP statement

Which statement is false about UDP?

A. UDP is used for management processes such as SNMP
B. UDP does not have any mechanism for flow control.
C. UDP provides congestion control like TCP.
D. UDP is a suitable transport protocol for multicasting.

Answer: C. UDP provides congestion control like TCP. UDP has no TCP-style congestion-control algorithm. The other choices fit UDP: SNMP commonly uses it, flow control is absent, and datagrams can support multicast.

Question 11, separating TCP control mechanisms (GATE Information Technology 2008)

Which of the following statements are TRUE?

(S1)  TCP handles both congestion and flow control

(S2)  UDP handles congestion but not flow control

(S3)  Fast retransmit deals with congestion but not flow control

(S4)  Slow start mechanism deals with both congestion and flow control

A. S1, S2 and S3 only
B. S1 and S3 only
C. S3 and S4 only
D. S1, S3 and S4 only

Answer: B. S1 and S3 only. TCP has receiver-window flow control and network-facing congestion control, so S1 is true. UDP supplies neither, making S2 false; fast retransmit concerns loss recovery and congestion response, so S3 is true. Slow start grows the congestion window, not the receiver's flow-control window, making S4 false.

Question 12, work performed by UDP (UGC NET December 2023)

The work done by UDP is / are :
(A) Congestion control
(B) Flow control
(C) Retransmission
(D) Segments transmission
Choose the correct answer from the options given below :

A. (A) and (D) Only
B. (C) Only
C. (D) Only
D. (B) and (C) Only

Answer: C. (D) Only. In this question's framing, UDP performs datagram transmission and port multiplexing. It supplies no congestion control, flow control, or retransmission; application reliability logic is not a UDP service.

6. UDP MCQ patterns and traps to revise

Revise protocol identification, application choice, handshake elimination, header arithmetic, and recognition of absent services.

• UDP is connectionless, but application logic can still maintain state.

• The UDP header is 8 bytes.

• UDP Length includes the header plus data.

• Window size is not a UDP header field.

• UDP has no built-in retransmission, flow control, or congestion control.

The earlier TCP and UDP MCQs: 12 Solved Transport Layer Questions uses the shared Question 11 within a mixed TCP-and-UDP set. Here, that question isolates UDP's lack of both controls, while the rest of this set focuses on UDP applications, header decoding, and datagram-length arithmetic. The TCP vs UDP: Transport Layer Explained owns the broader side-by-side protocol comparison.

7. UDP Protocol and Header MCQs: the short version and next step

Use two passes: answer all 12 without explanations, then redo the hexadecimal and length calculations from blank paper after one day. For broader study, use GATE Guidance by Sanchit Sir for structured GATE preparation, CS Fundamentals for Placements by Sanchit Sir for placement-oriented Computer Networks revision, or the GATE CS Exam Preparation category hub.