Netmask

A netmask is a string of 0’s and 1’s that screen out the network part of an IP address so that only the host computer part of the address remains. The binary 1’s at the beginning of the mask turn the network ID part of the IP address into 0’s. The binary 0’s that follow allow the host ID to remain. In a netmask, two bits are always automatically assigned. For example, in 255.255.225.0, “0” is the assigned network address, and in 255.255.255.255, “255” is the assigned broadcast address. The 0 and 255 are always assigned and cannot be used.