Why is subnet mask needed?

A subnet mask determines which part of an IP address belongs to the network and which part belongs to the host.

• Network division: Allows dividing large networks into smaller, manageable subnets.
• Routing: Helps routers determine which subnet the destination address is in and where to send traffic.
• Efficient use of IP addresses: Enables allocating the necessary number of IP addresses for each subnet, conserving the limited resource.
• Traffic control: Limits broadcast traffic within the subnet, increasing performance.

Example:

IP address: 192.168.1.100 Subnet mask: 255.255.255.0

In binary:

// IP address
11000000.10101000.00000001.01100100
// Subnet mask
11111111.11111111.11111111.00000000

The part where the mask has ones (the first three octets) defines the network address (192.168.1.0). The part where it has zeros (the last octet) defines the host address (0.0.0.100).