Subnetting and subnet masks in Computer Networks - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a subnet mask?

A subnet mask is a number that separates the IP address into the network part and the host part. It helps devices know which part of the address identifies the network and which part identifies the device.

beginner

Why do we use subnetting in networks?

Subnetting divides a large network into smaller parts called subnets. This helps organize the network better, improves security, and reduces traffic by limiting broadcast areas.

intermediate

How does a subnet mask look in binary?

A subnet mask is a series of 1s followed by 0s in binary. The 1s cover the network part, and the 0s cover the host part. For example, 255.255.255.0 in decimal is 11111111.11111111.11111111.00000000 in binary.

intermediate

What is the difference between a network address and a broadcast address?

The network address identifies the whole subnet and ends with all host bits set to 0. The broadcast address is used to send messages to all devices in the subnet and ends with all host bits set to 1.

intermediate

How do you calculate the number of hosts in a subnet?

The number of hosts is 2 to the power of the number of host bits minus 2. We subtract 2 because one address is for the network and one for the broadcast. For example, if there are 8 host bits, hosts = 2^8 - 2 = 254.

What does a subnet mask do?

A Connects two different networks

B Separates network and host parts of an IP address

C Encrypts network data

D Assigns IP addresses automatically

A subnet mask helps devices know which part of the IP address is the network and which part is the host.

Which of these is a valid subnet mask?

A 255.255.0.255

B 255.0.255.255

C 0.255.255.255

D 255.255.255.0

Subnet masks have continuous 1s followed by continuous 0s in binary. 255.255.255.0 fits this pattern.

What is the broadcast address used for?

A To send a message to all devices in a subnet

B To identify a single device

C To connect to the internet

D To encrypt data

The broadcast address allows sending messages to every device in the subnet at once.

If a subnet mask is 255.255.255.0, how many hosts can the subnet support?

A 255

B 256

C 254

D 512

With 8 host bits (32 - 24), the number of hosts is 2^8 - 2 = 254.

Why subtract 2 when calculating the number of hosts in a subnet?

A One address is for the network, one for broadcast

B To avoid IP conflicts

C Because two devices share one IP

D To save addresses for future use

The network address and broadcast address cannot be assigned to hosts, so they are excluded.

Explain what a subnet mask is and how it helps in a network.

Think about how devices know which part of the IP address is the network.

Describe the purpose of subnetting and how it benefits network management.

Consider why big networks might be hard to manage without subnetting.