IP Subnet Calculator

A subnet refers to a part of an IP protocol suite (internet protocol network). An IP network is a group of protocols used by the Internet. TCP/IP (Transmission Control Protocol/Internet Protocol) is the most common name.

Subnetting refers to the act of dividing a network into at least two distinct networks. Routers are devices that allow traffic interchange between subnetworks while also serving as a physical boundary. While IPv4 remains the most popular network addressing technology, IPv6 is growing in popularity.

An IP address consists of a routing number (prefix) and a host identifier (rest field). A rest field refers to an identifier that is unique to a particular host or network interface. Classless Inter-Domain Routing, (CIDR), is a common way to express a routing prefix. This works for IPv4 as well as IPv6. CIDR is used to create unique identifiers that can be used for both individual devices as well as networks. Subnet masks are also possible for IPv4 networks. These subnet masks are sometimes expressed in dot-decimal notation as seen in the Calculator's "Subnet" field. Every host on a subnetwork has the same network number, not the host ID, which is unique to each individual. These subnet masks can be used in IPv4 to distinguish between the host identifier and network number. IPv6's network prefix serves a similar function to the IPv4 subnet Mask. The prefix length is the number of bits in an address.

Before the introduction of CIDR, IPv4 prefixes could be obtained directly from the IP address based on the class (A-B or C) of the address. The network mask also affects the range of IP addresses it includes. However, to assign an address to a network address, one must have both its address and its mask.

Below is a table listing typical subnets that IPv4 uses: