Classful addressing (Class A, B, C) in Computer Networks - Mini Project: Build & Apply

Understanding Classful Addressing (Class A, B, C)

📖 Scenario: You are learning about how IP addresses were originally divided into classes to organize networks. This helps in understanding how computers identify each other on a network.

🎯 Goal: Create a simple reference table that shows the ranges and key features of Class A, Class B, and Class C IP addresses.

📋 What You'll Learn

Create a dictionary called ip_classes with keys 'Class A', 'Class B', and 'Class C'.

Each key should map to another dictionary with keys: range, default_subnet_mask, and max_hosts.

Add a variable called total_classes that counts how many classes are in ip_classes.

Create a list called class_names that contains the names of the classes from ip_classes.

Add a final statement that adds a new key description to each class dictionary with a short explanation.

💡 Why This Matters

🌍 Real World

Understanding classful addressing helps in grasping how networks were originally organized and how IP addresses are structured.

💼 Career

Network administrators and IT professionals use this knowledge to design and troubleshoot IP networks.

1

Create the IP classes dictionary

Create a dictionary called ip_classes with these exact keys and values:
'Class A' maps to {'range': '1.0.0.0 - 126.255.255.255', 'default_subnet_mask': '255.0.0.0', 'max_hosts': 16777214},
'Class B' maps to {'range': '128.0.0.0 - 191.255.255.255', 'default_subnet_mask': '255.255.0.0', 'max_hosts': 65534},
and 'Class C' maps to {'range': '192.0.0.0 - 223.255.255.255', 'default_subnet_mask': '255.255.255.0', 'max_hosts': 254}.

Computer Networks

# Create the ip_classes dictionary with Class A, B, and C details
# Your code here

Hint

Use a dictionary with keys 'Class A', 'Class B', and 'Class C'. Each key maps to another dictionary with the specified keys and values.

2

Add total_classes variable

Add a variable called total_classes that stores the number of classes in the ip_classes dictionary.

Computer Networks

ip_classes = {
    'Class A': {'range': '1.0.0.0 - 126.255.255.255', 'default_subnet_mask': '255.0.0.0', 'max_hosts': 16777214},
    'Class B': {'range': '128.0.0.0 - 191.255.255.255', 'default_subnet_mask': '255.255.0.0', 'max_hosts': 65534},
    'Class C': {'range': '192.0.0.0 - 223.255.255.255', 'default_subnet_mask': '255.255.255.0', 'max_hosts': 254}
}
# Add total_classes variable below
# Your code here

Hint

Use the len() function to count the number of keys in ip_classes.

3

Create list of class names

Create a list called class_names that contains the keys (class names) from the ip_classes dictionary.

Computer Networks

ip_classes = {
    'Class A': {'range': '1.0.0.0 - 126.255.255.255', 'default_subnet_mask': '255.0.0.0', 'max_hosts': 16777214},
    'Class B': {'range': '128.0.0.0 - 191.255.255.255', 'default_subnet_mask': '255.255.0.0', 'max_hosts': 65534},
    'Class C': {'range': '192.0.0.0 - 223.255.255.255', 'default_subnet_mask': '255.255.255.0', 'max_hosts': 254}
}
total_classes = len(ip_classes)
# Create class_names list below
# Your code here

Hint

Use the keys() method on ip_classes and convert it to a list.

4

Add descriptions to each class

Add a new key called description to each class dictionary inside ip_classes with these exact values:
'Class A': 'Supports very large networks with many hosts',
'Class B': 'Used for medium-sized networks',
'Class C': 'Designed for small networks with fewer hosts'.

Computer Networks

ip_classes = {
    'Class A': {'range': '1.0.0.0 - 126.255.255.255', 'default_subnet_mask': '255.0.0.0', 'max_hosts': 16777214},
    'Class B': {'range': '128.0.0.0 - 191.255.255.255', 'default_subnet_mask': '255.255.0.0', 'max_hosts': 65534},
    'Class C': {'range': '192.0.0.0 - 223.255.255.255', 'default_subnet_mask': '255.255.255.0', 'max_hosts': 254}
}
total_classes = len(ip_classes)
class_names = list(ip_classes.keys())
# Add description key to each class dictionary below
# Your code here

Hint

Add the description key with the exact text to each class dictionary inside ip_classes.

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