255.255.255.0

Definition: 255.255.255.0 is the most common subnet mask used on computers connected to Internet Protocol (IP) networks. An incorrectly configured subnet mask (also called netmask) causes some types of network connection failures.

255.255.255.0 and Alternate Subnet Notation

The subnet mask 255.255.255.0 is also written as a 32-bit binary number:

11111111 11111111 11111111 00000000

The '0' digits of the mask span the IP range of the subnet, 8 bits or 255 addresses in this case.

In classless IP networks, the subnet representation is converted to a shorthand notation based on the number of '1' digits in the mask. In this case, /24.

Using 255.255.255.0 As An IP Address

Although it is the form of an IP address number, networks devices can only use 255.255.255.0 as a subnet mask and not as a working IP address. Attempting to use this number (or any IP number that starts with 255) as a device address will cause the IP network connection to fail due to the definition of number ranges on IP networks.