Internet Protocol version 4 (IPv4) defines an IP address as a 32-bit number. However, because of the growth of the Internet and the depletion of available IPv4 addresses, a new version of IP (IPv6), using 128 bits for the IP address, was developed in 1995, and standardized in December 1998. In July 2017, a final definition of the protocol was published. IPv6 deployment has been ongoing since the mid-2000s.

         IP addresses are usually written and displayed in human-readable notations, such as 172.16.254.1 in IPv4, and 2001:db8:0:1234:0:567:8:1 in IPv6. The size of the routing prefix of the address is designated in CIDR notation by suffixing the address with the number of significant bits, e.g., 192.168.1.15/24, which is equivalent to the historically used subnet mask 255.255.255.0.

Sample IP Address
- Class A 10.xxx.xxx.xxx
- Class B 172.16.xxx.xxx To 172.31.xxx.xxx
- Class C 192.168.0.xxx To 192.168.255.xxx