An IP subnet, or “subnetwork”, is a subsection of a larger IP network. Subnets exist as a means of partitioning large networks into more manageable sections. A subnet contains a specific range of IP addresses assigned to devices in use together, for instance, in a specific company department.
How do IP subnets work?
For the sake of simplicity, a subnet can be compared to a district in a city. In much the same way that cities use area codes to differentiate between districts and deliver mail efficiently, IPs are used to differentiate subnetworks on a larger network. Just as area codes make mail delivery simpler, the use of IP subnets makes the routing of data packets simpler and more efficient.
Devices that are in are in the same subnet will have the same prefix, and communication between subnets is handled by a router.
What is the difference between an IP address and a subnet?
An IP (Internet Protocol) address is a unique identifier code assigned to each device on a network. Each address is comprised of a 32-bit sequence of four numbers, called octets. Each octet ranges from 0 to 255, and each is separated by a decimal point. IPs can range from 0.0.0.0 to 255.255.255.255.
A subnet is a partition which contains a group of IPs, and this is expressed through the addition of a subnet mask, for example ‘/24’. An example would be ‘198.168.123.132 /24’. The /24 indicates the number of bits in an IP address which are fixed to determine the subnet, with the remaining bits assigned separately to each device in the subnet.
How many IP addresses are in each subnet?
In a typical class C IPv4 space with a 24-bit network portion and an 8-bit host portion, a /24 subnet would contain 256 addresses, 254 of which are usable.
The number of addresses in a subnet is dependent on the subnet length, however. Longer subnet length means more fixed bits and fewer bits for allocating to network devices. Conversely, shorter subnet lengths occupy a larger portion of a network, leaving more space for individual addresses within that subnet.
