Subnetting MCQs

1. What is the purpose of subnetting in networking?

a) To reduce network congestion b) To divide a larger network into smaller subnetworks c) To increase IP address utilization efficiency d) Both b and c

Correct Answer: d) Both b and c

Explanation:
Subnetting serves multiple purposes: dividing large networks into smaller, more manageable subnetworks (improving organization and security) and increasing IP address utilization efficiency (reducing wasted addresses). While it can indirectly reduce congestion, that's not its primary purpose.

2. Which of the following best describes subnetting?

a) Combining multiple networks into a single large network b) Splitting a larger network into multiple smaller networks c) Assigning private IP addresses to all devices d) Converting IPv4 addresses to IPv6

Correct Answer: b) Splitting a larger network into multiple smaller networks

Explanation:
Subnetting is the process of dividing a single large network into multiple smaller logical subnetworks (subnets). This is achieved by borrowing bits from the host portion of an IP address to create additional network bits.

3. What is the formula to calculate the number of subnets?

a) 2ⁿ (where n is the number of borrowed bits) b) 2^h-2 (where h is the number of host bits) c) 2ⁿ-2 (where n is the number of subnet bits) d) 2^h

Correct Answer: a) 2ⁿ (where n is the number of borrowed bits)

Explanation:
The number of subnets created is calculated as 2 raised to the power of the number of bits borrowed from the host portion (n). For example, borrowing 3 bits creates 2³ = 8 subnets. Modern implementations typically don't subtract 2 (unlike host calculation).

4. In subnetting, what does the subnet mask define?

a) The number of available IP addresses b) The network and host portions of an IP address c) The number of total hosts d) The MAC address of the router

Correct Answer: b) The network and host portions of an IP address

Explanation:
The subnet mask is a 32-bit number that distinguishes the network portion from the host portion of an IP address. The 1s in the mask represent the network bits, and the 0s represent the host bits.

5. How many subnets can be created with a /26 subnet mask?

a) 2 b) 4 c) 8 d) 64

Correct Answer: c) 8

Explanation:
For a /26 subnet mask on a /24 network (default Class C), we've borrowed 2 bits (26-24=2). Number of subnets = 2² = 4. However, if considering the original classful boundaries (Class A/B), the calculation would differ. The answer assumes a /24 starting network.

6. What is the subnet mask for 192.168.1.0/28?

a) 255.255.255.192 b) 255.255.255.224 c) 255.255.255.240 d) 255.255.255.248

Correct Answer: c) 255.255.255.240

Explanation:
A /28 subnet mask has 28 network bits. In the fourth octet: 11110000 (240 in decimal). The full subnet mask is therefore 255.255.255.240.

7. How many usable IP addresses are available in a /27 subnet?

a) 30 b) 32 c) 62 d) 126

Correct Answer: a) 30

Explanation:
A /27 subnet has 5 host bits (32-27). Total addresses = 2⁵ = 32. Subtract 2 for network and broadcast addresses, leaving 30 usable host addresses.

8. What is the broadcast address of the 192.168.1.64/26 subnet?

a) 192.168.1.63 b) 192.168.1.127 c) 192.168.1.128 d) 192.168.1.255

Correct Answer: b) 192.168.1.127

Explanation:
For 192.168.1.64/26: - Network address: 192.168.1.64 - Next network: 192.168.1.128 - Broadcast is one less than next network: 192.168.1.127

9. What is the first usable host address in the 172.16.5.0/24 subnet?

a) 172.16.5.1 b) 172.16.5.0 c) 172.16.5.255 d) 172.16.5.2

Correct Answer: a) 172.16.5.1

Explanation:
In any subnet: - First address is the network address (172.16.5.0) - Second address is the first usable host (172.16.5.1) - Last address is the broadcast (172.16.5.255)

10. How many subnets can be created if 192.168.1.0/24 is subnetted into /29?

a) 8 b) 16 c) 32 d) 64

Correct Answer: c) 32

Explanation:
Borrowed bits = 29-24 = 5 bits Number of subnets = 2⁵ = 32 Each subnet will have 8 total addresses (2³), with 6 usable hosts

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