Subnetting is the process of dividing a network into smaller sub-networks or subnets. This is done by taking a portion of the host portion of the IP address and using it to identify the subnet. Subnetting allows network administrators to more efficiently use their IP address space and manage their networks.
Here is a great video on subnetting. Feel free to watch this short video.
Subnetting is accomplished by using a subnet mask, which is a 32-bit value that is used to divide an IP address into a network portion and a host portion. The subnet mask is usually expressed in dotted decimal notation, just like an IP address.
For example, consider the IP address 192.168.1.1 with a subnet mask of 255.255.255.0. In binary, the IP address and subnet mask would be:
IP address: 11000000.10101000.00000001.00000001 Subnet mask: 11111111.11111111.11111111.00000000
The first 24 bits (or 3 octets) of the IP address are used to identify the network, while the last 8 bits (or 1 octet) are used to identify the host. The subnet mask shows which bits are used for the network portion and which bits are used for the host portion. In this example, the first 24 bits are used for the network and the last 8 bits are used for the host.
By using subnetting, we can further divide the network into smaller subnets. For example, we could use a subnet mask of 255.255.255.128, which would reserve the first 25 bits (or 3.5 octets) for the network and the last 7 bits (or 0.5 octets) for the host. This would create two subnets, each with 126 host addresses. We could also use a subnet mask of 255.255.255.192, which would reserve the first 26 bits (or 3.25 octets) for the network and the last 6 bits (or 0.75 octets) for the host. This would create four subnets, each with 62 host addresses.
In summary, subnetting allows network administrators to divide a network into smaller subnets, which can improve network performance, security, and management. Subnetting is accomplished by using a subnet mask, which determines how many bits are used for the network portion and how many bits are used for the host portion of an IP address.