UDP datagram structure in Computer Networks - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to identify the size of the UDP header in bytes.

Computer Networks

UDP header size is [1] bytes.

Drag options to blanks, or click blank then click option'

A20

B8

C16

D12

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing UDP header size with IP header size.

Assuming UDP header size varies.

The UDP header is always 8 bytes long, which includes source port, destination port, length, and checksum fields.

2fill in blank

medium

Complete the code to name the first field in the UDP header.

Computer Networks

The first field in the UDP header is the [1].

Drag options to blanks, or click blank then click option'

ASource Port

BDestination Port

CLength

DChecksum

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up source and destination ports.

Choosing checksum as the first field.

The first field in the UDP header is the Source Port, which identifies the sender's port number.

3fill in blank

hard

Fix the error in the UDP header field order: Source Port, Length, Destination Port, {{BLANK_1}}.

Computer Networks

The correct order is Source Port, Destination Port, Length, [1].

Drag options to blanks, or click blank then click option'

AChecksum

BData

CProtocol

DHeader Length

Attempts:

3 left

💡 Hint

Common Mistakes

Placing Length after Destination Port incorrectly.

Confusing checksum with protocol field.

The UDP header fields are ordered as Source Port, Destination Port, Length, and Checksum.

4fill in blank

hard

Fill both blanks to complete the UDP header fields: {{BLANK_1}}, {{BLANK_2}}, Length, Checksum.

Computer Networks

UDP header fields start with [1] and [2], followed by Length and Checksum.

Drag options to blanks, or click blank then click option'

ASource Port

BData

CDestination Port

DProtocol

Attempts:

3 left

💡 Hint

Common Mistakes

Using Data or Protocol as header fields.

Swapping Source and Destination Port order.

The UDP header starts with Source Port and Destination Port fields, then Length and Checksum.

5fill in blank

hard

Fill all three blanks to complete the UDP datagram structure: {{BLANK_1}}, {{BLANK_2}}, {{BLANK_3}}.

Computer Networks

UDP datagram consists of [1], [2], [3], and Payload.

Drag options to blanks, or click blank then click option'

AHeader

BChecksum

CLength

DSource Port

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing Source Port as a separate part of the datagram.

Omitting the Length or Checksum fields.

The UDP datagram consists of the Header (including Length and Checksum fields), and the Payload data.

Practice

1. Which of the following is NOT a field in the UDP datagram header?

easy

A. Sequence Number

B. Destination Port

C. Source Port

D. Checksum

Solution

1. Step 1: Recall UDP header fields

   The UDP header contains Source Port, Destination Port, Length, and Checksum fields.

2. Step 2: Identify the incorrect field

   Sequence Number is a field in TCP, not UDP.

3. Final Answer:

   Sequence Number -> Option A

4. Quick Check:

   UDP header fields exclude Sequence Number [OK]

Hint: Remember UDP header has no sequence number, unlike TCP [OK]

Common Mistakes:

• Confusing UDP with TCP header fields
• Thinking UDP has sequence numbers
• Mixing checksum with sequence number

2. What is the total size in bytes of the UDP header?

easy

A. 8 bytes

B. 4 bytes

C. 12 bytes

D. 16 bytes

Solution

1. Step 1: Recall UDP header size

   The UDP header consists of four fields, each 2 bytes long: Source Port, Destination Port, Length, and Checksum.

2. Step 2: Calculate total size

   4 fields x 2 bytes each = 8 bytes total.

3. Final Answer:

   8 bytes -> Option A

4. Quick Check:

   4 fields x 2 bytes = 8 bytes [OK]

Hint: UDP header always 8 bytes, fixed size [OK]

Common Mistakes:

• Confusing with IP or TCP header size
• Assuming variable header size
• Counting data length as header size

3. Given a UDP datagram with Source Port = 1234, Destination Port = 80, Length = 20, and Checksum = 0x1A2B, which field indicates the size of the entire UDP datagram including header and data?

medium

A. Source Port

B. Checksum

C. Destination Port

D. Length

Solution

1. Step 1: Understand UDP Length field meaning

   The Length field specifies the total length of the UDP datagram, including header and data, in bytes.

2. Step 2: Identify the field indicating size

   Among the given fields, only Length represents the size of the entire UDP datagram.

3. Final Answer:

   Length -> Option D

4. Quick Check:

   Length field = total UDP datagram size [OK]

Hint: Length field shows total UDP datagram size [OK]

Common Mistakes:

• Confusing port numbers with size
• Thinking checksum indicates size
• Ignoring header size in length

4. A programmer wrote code to parse a UDP datagram but forgot to read the Checksum field. What is the likely consequence?

medium

A. The datagram will be rejected by the receiver

B. The length field will be misinterpreted

C. The datagram may be accepted without error checking

D. The source port will be incorrect

Solution

1. Step 1: Understand role of Checksum in UDP

   The Checksum is used for error checking but is optional in IPv4; ignoring it means no error verification.

2. Step 2: Consequence of ignoring Checksum

   If the Checksum is not read or verified, the datagram may still be accepted but without error checking, risking corrupted data.

3. Final Answer:

   The datagram may be accepted without error checking -> Option C

4. Quick Check:

   Ignoring checksum skips error check but datagram accepted [OK]

Hint: Ignoring checksum skips error check, datagram still accepted [OK]

Common Mistakes:

• Assuming datagram is rejected
• Confusing checksum with port fields
• Thinking length is affected

5. You need to design a simple application that sends small messages quickly without guaranteed delivery. Which UDP datagram feature makes it suitable for this?

hard

A. Automatic retransmission of lost packets

B. Fixed 8-byte header with no connection setup

C. Sequence numbers for ordered delivery

D. Built-in encryption for security

Solution

1. Step 1: Identify UDP features for fast, simple messaging

   UDP uses a fixed 8-byte header and does not require connection setup, enabling quick transmission.

2. Step 2: Eliminate incorrect features

   UDP does not provide sequence numbers, retransmission, or encryption by default.

3. Final Answer:

   Fixed 8-byte header with no connection setup -> Option B

4. Quick Check:

   UDP's simple header and no handshake enable fast messaging [OK]

Hint: UDP's simple header and no handshake enable fast messaging [OK]

Common Mistakes:

• Confusing UDP with TCP features
• Expecting retransmission or ordering
• Assuming built-in security