Classful addressing (Class A, B, C) in Computer Networks - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to identify the class of an IP address based on its first octet.

Computer Networks

if 1 <= first_octet <= [1]:
    ip_class = 'A'

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

A127

B255

C126

D128

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 127 or 128 as the upper limit for Class A.

Class A IP addresses have their first octet in the range 1 to 126.

2fill in blank

medium

Complete the code to check if an IP address belongs to Class B based on its first octet.

Computer Networks

if [1] <= first_octet <= 191:
    ip_class = 'B'

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

A255

B192

C126

D128

Attempts:

3 left

💡 Hint

Common Mistakes

Using 192 as the lower bound instead of 128.

Class B IP addresses have their first octet between 128 and 191.

3fill in blank

hard

Fix the error in the code to correctly identify Class C IP addresses.

Computer Networks

if 192 <= first_octet <= [1]:
    ip_class = 'C'

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

A223

B224

C191

D255

Attempts:

3 left

💡 Hint

Common Mistakes

Using 224 or 255 as the upper limit for Class C.

Class C IP addresses have their first octet between 192 and 223.

4fill in blank

hard

Fill both blanks to complete the code that determines the class of an IP address based on its first octet.

Computer Networks

if first_octet >= [1] and first_octet <= [2]:
    ip_class = 'B'

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

A128

B191

C223

D126

Attempts:

3 left

💡 Hint

Common Mistakes

Using 126 or 223 as bounds for Class B.

Class B IP addresses range from 128 to 191 in the first octet.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps IP classes to their first octet ranges.

Computer Networks

ip_classes = {
    'A': (1, [1]),
    'B': ([2], [3]),
    'C': (192, 223)
}

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

A126

B128

C191

D224

Attempts:

3 left

💡 Hint

Common Mistakes

Using 127 or 224 in the ranges incorrectly.

The ranges are:
Class A: 1-126
Class B: 128-191
Class C: 192-223

Practice

1. Which class of IP address has the first octet range from 1 to 126?

easy

A. Class D

B. Class B

C. Class C

D. Class A

Solution

1. Step 1: Understand IP class ranges

   Class A addresses have the first octet from 1 to 126.

2. Step 2: Match the range to the class

   Since 1-126 matches Class A, this is the correct class.

3. Final Answer:

   Class A -> Option D

4. Quick Check:

   1-126 = Class A [OK]

Hint: Class A starts with 1-126 in first octet [OK]

Common Mistakes:

• Confusing Class A with Class B range
• Including 0 or 127 in Class A range
• Mixing Class D with Class A

2. Which of the following is the correct subnet mask for a Class B IP address?

easy

A. 255.0.0.0

B. 255.255.255.0

C. 255.255.0.0

D. 255.255.255.255

Solution

1. Step 1: Recall subnet masks for classes

   Class A uses 255.0.0.0, Class B uses 255.255.0.0, Class C uses 255.255.255.0.

2. Step 2: Identify Class B subnet mask

   The correct subnet mask for Class B is 255.255.0.0.

3. Final Answer:

   255.255.0.0 -> Option C

4. Quick Check:

   Class B mask = 255.255.0.0 [OK]

Hint: Class B mask has two 255 blocks at start [OK]

Common Mistakes:

• Choosing Class A or C subnet masks for Class B
• Confusing subnet mask with broadcast address
• Selecting 255.255.255.255 which is a host mask

3. What is the network class of the IP address 192.168.1.1?

medium

A. Class C

B. Class B

C. Class D

D. Class A

Solution

1. Step 1: Check the first octet of the IP

   The first octet is 192.

2. Step 2: Match first octet to class range

   Class C addresses range from 192 to 223, so 192.168.1.1 is Class C.

3. Final Answer:

   Class C -> Option A

4. Quick Check:

   192 in 192-223 = Class C [OK]

Hint: 192-223 first octet means Class C [OK]

Common Mistakes:

• Mistaking Class B range for Class C
• Confusing Class D (224-239) with Class C
• Ignoring the first octet range

4. Identify the error in this IP address classification: IP: 130.25.10.5 classified as Class C.

medium

A. 130.25.10.5 is Class B, not Class C

B. 130.25.10.5 is Class A, not Class C

C. 130.25.10.5 is Class C, classification is correct

D. 130.25.10.5 is Class D, not Class C

Solution

1. Step 1: Check the first octet of the IP

   The first octet is 130.

2. Step 2: Determine correct class range

   Class B ranges from 128 to 191, so 130.25.10.5 is Class B, not Class C.

3. Final Answer:

   130.25.10.5 is Class B, not Class C -> Option A

4. Quick Check:

   130 in 128-191 = Class B [OK]

Hint: 130 is in Class B range 128-191 [OK]

Common Mistakes:

• Classifying 130 as Class C (192-223)
• Confusing Class A and B ranges
• Ignoring first octet value

5. You have an IP address 10.0.0.1 and want to divide it into smaller networks. Which classful address and default subnet mask does it belong to, and how many hosts can each subnet support?

hard

A. Class B, 255.255.0.0, supports about 65,000 hosts

B. Class A, 255.0.0.0, supports about 16 million hosts

C. Class C, 255.255.255.0, supports about 254 hosts

D. Class D, no subnet mask, used for multicast

Solution

1. Step 1: Identify the class of IP 10.0.0.1

   The first octet is 10, which falls in Class A (1-126).

2. Step 2: Recall default subnet mask and host count for Class A

   Class A default mask is 255.0.0.0, allowing 2^24 - 2 = 16,777,214 hosts approximately.

3. Final Answer:

   Class A, 255.0.0.0, supports about 16 million hosts -> Option B

4. Quick Check:

   10 in 1-126 = Class A, hosts ≈ 16 million [OK]

Hint: Class A IPs start 1-126, huge host capacity [OK]

Common Mistakes:

• Confusing Class A with Class B or C
• Using wrong subnet mask for Class A
• Miscounting number of hosts