How Can I Find Out If a Host IP Address Is Valid or Invalid?

A basic understanding of what IP addresses represent can help to determine their validity. There are also free utilities available on the web that allow users to enter a specific IP address to determine the network and broadcast addresses of a given IP.

An IP address is a 32-bit code that identifies the computer or other device to a TCP/IP network. The 32-bit code consists of four octets, also known as IPv4. The octets are converted to a dotted decimal format, resulting in a series of four numbers separated by dots. The first three numbers represent the network. The last number represents the host.

Valid IP addresses follow certain protocols.

  • Class A or large networks: to
  • Class B or medium sized networks: to
  • Class C or small networks: to

There are certain clues that immediately indicate that an IP address is invalid.

  • The number 255 should not appear in any of the octets.
  • The number 0 cannot be the first or the last number (host number) in the IP address.
  • Exception: the number is used by hosts which do not know their IP address.

The number 255 is reserved for broadcast addressing and is used in the subnet mask, which is a code used by a TCP/IP network to determine if the host is on a remote network or not.