An Internet Protocol (IP) address is a numerical identifier assigned to any network device (e.g. computer, router) that communicates using IP. IP addresses follow standards as set out by the Internet Engineering Task Force (IETF). As of this writing, the two standards in common use are IP version 4 (IPv4) and IP version 6 (IPv6).
IP Version 4 (IPv4)
IPv4 specifies an IP address as a 32-bit number, displayed most commonly in dotted decimal format (e.g. 1.2.3.4) for easier human readability. The dotted decimal format is also known as a quad octet, as it represents four (quad) groups of eight bits (octet).
Example:
An IP address, displayed as 32-bit number: 10101010101010101010101010101010
Same IP address, displayed in dotted decimal format: 170.170.170.170
Reserved IP Addresses
Some IP addresses are reserved to serve a special purpose and should not be assigned to any network device. These IP addresses are:
0.0.0.0 - Default gateway
255.255.255.255 - Broadcast
127.0.0.1 - Local host / loopback
IP Version 6 (IPv6)
IPv6 specifies an IP address as a 128-bit number, displayed most commonly in eight groups of four hexadecimal strings separated by colons.
Example:
An IPv4 address: 128.128.128.128
An IPv6 address: 0123:4567:89ab:cdef:0123:4567:89ab:cdef