Subnet Mask

A subnet mask is a crucial component in IP networking that helps to divide an IP address into two parts: the network portion and the host portion. It essentially determines which part of an IP address refers to the network itself and which part refers to the specific device or host on that network.

Here's a breakdown of how it works:

1. IP Address: An IP address (e.g., 192.168.1.1) is a 32-bit number typically written in dotted decimal format. It’s divided into four octets, each containing 8 bits.

2. Subnet Mask: The subnet mask (e.g., 255.255.255.0) also consists of 32 bits and is used to mask the IP address. It has a similar format to the IP address, but the bits are set to either 1 or 0. The 1s cover the network part of the IP address, while the 0s cover the host part.

3. Network and Host Portions:
- Network Portion: This is identified by the bits set to 1 in the subnet mask. It tells you which part of the IP address specifies the network.
- Host Portion: This is identified by the bits set to 0 in the subnet mask. It tells you which part of the IP address specifies the individual device within that network.

Example:

IP Address: 192.168.1.10
Subnet Mask: 255.255.255.0

In binary:
- IP Address: 11000000.10101000.00000001.00001010
- Subnet Mask: 11111111.11111111.11111111.00000000

Applying the subnet mask:
- The network part (all bits of the IP address where the subnet mask has 1s) is 192.168.1.0.
- The host part (all bits of the IP address where the subnet mask has 0s) is 0.0.0.10.

So, 192.168.1.10 is part of the 192.168.1.0 network, and the specific host is 10 within that network.

Subnet masks are essential for routing traffic within a network and for determining how large the network can be (i.e., how many devices can be accommodated).

Source: Wikipedia®