Subnetting and subnet masks in Computer Networks - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to calculate the number of hosts in a subnet given the subnet mask bits.

Computer Networks

hosts = (2 ** (32 - [1])) - 2

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

A24

B26

C16

D30

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to subtract 2 for network and broadcast addresses.

Using the subnet mask bits directly instead of subtracting from 32.

The subnet mask bits represent the network portion. Subtracting from 32 gives the host bits. The number of hosts is 2 to the power of host bits minus 2 (for network and broadcast addresses).

2fill in blank

medium

Complete the code to find the subnet mask in dotted decimal notation from the number of mask bits.

Computer Networks

mask = [[1] for i in range(4)]

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

A0

B128

C192

D255

Attempts:

3 left

💡 Hint

Common Mistakes

Using 128 or 192 for all bytes instead of 255 for full bytes.

Confusing mask bits with decimal values.

Each full byte in the subnet mask is 255 in decimal. For example, a /24 mask has three full bytes of 255.

3fill in blank

hard

Fix the error in the code to calculate the number of subnets given the borrowed bits.

Computer Networks

subnets = 2 ** [1]

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

Ahost_bits

Bborrowed_bits

Cmask_bits

Dnetwork_bits

Attempts:

3 left

💡 Hint

Common Mistakes

Using host bits or mask bits instead of borrowed bits.

Confusing network bits with borrowed bits.

The number of subnets is 2 raised to the power of the number of bits borrowed from the host portion.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps subnet numbers to their subnet masks in binary.

Computer Networks

subnet_masks = {n: bin(255 << (8 - [1])) for n in range([2])}

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

Aborrowed_bits

Bhost_bits

Csubnets

Dmask_bits

Attempts:

3 left

💡 Hint

Common Mistakes

Using host bits or mask bits incorrectly in the shift.

Using mask bits instead of number of subnets in range.

The subnet mask for each subnet is calculated by shifting 255 left by (8 - borrowed_bits). The range is the number of subnets.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps subnet numbers to their broadcast addresses.

Computer Networks

broadcasts = {n: network_base + ([1] * n) + [2] for n in range([3])}

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

Asubnet_size

Bsubnet_size - 1

Cnumber_of_subnets

Dhost_bits

Attempts:

3 left

💡 Hint

Common Mistakes

Using host bits instead of subnet size.

Confusing number of subnets with host bits.

The broadcast address for each subnet is calculated by adding the subnet size times the subnet number plus subnet size minus one to the network base. The range is the number of subnets.

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