Classful addressing (Class A, B, C) in Computer Networks - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Identify the Class of an IP Address

Given the IP address 130.25.50.1, which class does it belong to?

A Class C

B Class B

C Class A

D Class D

💡 Hint

Look at the first number in the IP address and compare it to the class ranges.

The first octet is 130, which falls between 128 and 191. This range corresponds to Class B addresses.

📋 Factual

intermediate

Number of Hosts in Class C Network

How many usable host addresses are available in a Class C network?

A 254

B 256

C 65534

D 16,777,214

💡 Hint

Remember to subtract network and broadcast addresses from total hosts.

Class C networks have 8 bits for hosts, so 2^8 = 256 addresses. Subtracting 2 for network and broadcast leaves 254 usable hosts.

🔍 Analysis

advanced

Determine Network Class from Binary

The first octet of an IP address in binary is 01100010. What is the class of this IP address?

A Class A

B Class E

C Class C

D Class B

💡 Hint

Check the first few bits to identify the class.

Class A addresses start with 0, Class B with 10, Class C with 110. The binary 01100010 starts with 0 and then 1, which is decimal 98. Since 98 is between 128 and 191? No, 98 is between 1 and 126, so Class A. But the binary starts with 0, so Class A.

❓ Comparison

advanced

Compare Network Sizes of Class A and Class B

Which statement correctly compares the number of possible hosts in Class A and Class B networks?

A Class A supports more hosts than Class B because it has more host bits.

B Class B supports more hosts than Class A because it has more network bits.

C Class A and Class B support the same number of hosts.

D Class B supports more hosts than Class A because it has fewer network bits.

💡 Hint

Think about how many bits are used for hosts in each class.

Class A uses 24 bits for hosts, Class B uses 16 bits. More host bits mean more hosts.

❓ Reasoning

expert

Identify the Class from IP Range and Explain

An organization has an IP address starting with 192.168.5.10. Which class does this IP belong to and why is it commonly used in private networks?

A Class A; because it allows many hosts and is reserved for private use.

B Class B; because it balances network and host bits and is public.

C Class C; because it has a smaller network size and is reserved for private use.

D Class D; because it is used for multicast and private addressing.

💡 Hint

Check the first octet range and recall private IP address ranges.

192.168.x.x addresses are Class C and are part of private IP ranges used inside local networks.

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