Subnetting and subnet masks in Computer Networks - Mini Project: Build & Apply

Subnetting and Subnet Masks

📖 Scenario: You are working as a network technician setting up a small office network. You need to divide a single IP network into smaller subnetworks to organize different departments.

🎯 Goal: Build a simple subnetting plan by creating the original network, defining the subnet mask, calculating subnet addresses, and identifying the broadcast address for each subnet.

📋 What You'll Learn

Create a variable for the original IP network address

Create a variable for the subnet mask

Calculate subnet addresses using the subnet mask

Identify the broadcast address for each subnet

💡 Why This Matters

🌍 Real World

Subnetting helps organize and secure networks by dividing large networks into smaller, manageable parts.

💼 Career

Network administrators and IT professionals use subnetting to design efficient and secure networks.

1

Define the Original Network Address

Create a variable called network_address and set it to the string "192.168.1.0" representing the original IP network address.

Computer Networks

# Create the original network address
# Your code here

Hint

The network address is the starting point for subnetting. Use a string to store it.

2

Set the Subnet Mask

Create a variable called subnet_mask and set it to the string "255.255.255.192" which will divide the network into four subnets.

Computer Networks

network_address = "192.168.1.0"
# Define the subnet mask
# Your code here

Hint

The subnet mask determines how many subnets you create. Use the correct mask for four subnets.

3

Calculate Subnet Addresses

Create a list called subnets containing the four subnet addresses as strings: "192.168.1.0", "192.168.1.64", "192.168.1.128", and "192.168.1.192".

Computer Networks

network_address = "192.168.1.0"
subnet_mask = "255.255.255.192"
# List the subnet addresses
# Your code here

Hint

Each subnet starts at a multiple of 64 in the last part of the IP address.

4

Identify Broadcast Addresses

Create a list called broadcast_addresses containing the broadcast addresses for each subnet as strings: "192.168.1.63", "192.168.1.127", "192.168.1.191", and "192.168.1.255".

Computer Networks

network_address = "192.168.1.0"
subnet_mask = "255.255.255.192"
subnets = ["192.168.1.0", "192.168.1.64", "192.168.1.128", "192.168.1.192"]
# List the broadcast addresses
# Your code here

Hint

The broadcast address is the last IP in each subnet range.

Practice

1. What is the main purpose of subnetting in computer networks?

easy

A. To connect different types of devices without IP addresses

B. To increase the total number of IP addresses available globally

C. To encrypt data sent over the network

D. To divide a large network into smaller, manageable parts

Solution

1. Step 1: Understand subnetting concept

   Subnetting is used to split a large network into smaller subnetworks for easier management.

2. Step 2: Compare options

   Only To divide a large network into smaller, manageable parts correctly describes subnetting's purpose; others describe unrelated functions.

3. Final Answer:

   To divide a large network into smaller, manageable parts -> Option D

4. Quick Check:

   Subnetting = dividing networks [OK]

Hint: Subnetting means splitting networks into smaller parts [OK]

Common Mistakes:

• Confusing subnetting with encryption
• Thinking subnetting increases global IP addresses
• Believing subnetting connects devices without IPs

2. Which of the following is a valid subnet mask?

easy

A. 255.255.255.0

B. 0.255.255.255

C. 255.0.255.0

D. 255.255.0.255

Solution

1. Step 1: Recall valid subnet mask format

   A subnet mask must have continuous 1s followed by continuous 0s in binary, like 255.255.255.0.

2. Step 2: Check each option

   Only 255.255.255.0 fits this rule; others have mixed or invalid patterns.

3. Final Answer:

   255.255.255.0 -> Option A

4. Quick Check:

   Valid subnet mask = continuous 1s then 0s [OK]

Hint: Subnet masks have continuous 255s then 0s [OK]

Common Mistakes:

• Choosing masks with mixed 255 and 0 in wrong order
• Not knowing binary pattern rules for subnet masks
• Confusing IP addresses with subnet masks

3. Given the IP address 192.168.1.10 and subnet mask 255.255.255.0, what is the network address?

medium

A. 192.168.1.0

B. 192.168.0.0

C. 192.168.1.255

D. 192.168.0.255

Solution

1. Step 1: Understand network address calculation

   The network address is found by performing a bitwise AND between the IP address and subnet mask.

2. Step 2: Calculate network address

   IP: 192.168.1.10 AND Mask: 255.255.255.0 gives 192.168.1.0 as the network address.

3. Final Answer:

   192.168.1.0 -> Option A

4. Quick Check:

   Network address = IP AND subnet mask [OK]

Hint: AND IP with mask to get network address [OK]

Common Mistakes:

• Confusing broadcast address with network address
• Using wrong subnet mask for calculation
• Not applying bitwise AND operation

4. Identify the error in this subnet mask: 255.255.224.255

medium

A. Subnet mask must always end with 0 in the last octet

B. Subnet mask cannot have 224 in any octet

C. Subnet mask must have continuous 1s followed by 0s; this mask breaks that rule

D. Subnet mask cannot have more than two 255 octets

Solution

1. Step 1: Check binary pattern of subnet mask

   Subnet masks must have all 1s on the left side and all 0s on the right side without interruption.

2. Step 2: Analyze given mask

   255.255.224.255 breaks this rule because the last octet is 255 (all 1s) after 224 (which is partial 1s), causing non-continuous 1s.

3. Final Answer:

   Subnet mask must have continuous 1s followed by 0s; this mask breaks that rule -> Option C

4. Quick Check:

   Subnet mask = continuous 1s then 0s [OK]

Hint: Subnet mask 1s must be continuous, no breaks [OK]

Common Mistakes:

• Thinking 224 is invalid in subnet masks
• Believing last octet must always be 0
• Ignoring binary continuity rule

5. You have a network 10.0.0.0/24 and need at least 6 subnets. Which subnet mask should you use to create enough subnets?

hard

A. 255.255.255.192

B. 255.255.255.224

C. 255.255.255.0

D. 255.255.255.128

Solution

1. Step 1: Calculate required subnet bits

   To create at least 6 subnets, find minimum bits n where 2^n ≥ 6. Here, n=3 (2^3=8 subnets).

2. Step 2: Determine new subnet mask

   Original mask /24 means 24 bits for network. Adding 3 bits for subnetting gives /27 mask.

3. Step 3: Convert /27 to subnet mask

   /27 corresponds to 255.255.255.224.

4. Final Answer:

   255.255.255.224 -> Option B

5. Quick Check:

   3 subnet bits = /27 = 255.255.255.224 [OK]

Hint: Use 2^n ≥ needed subnets to find mask [OK]

Common Mistakes:

• Choosing mask with too few subnet bits
• Confusing host bits with subnet bits
• Not converting CIDR to decimal mask correctly