A netmask is a binary number, usually stored in decimal, applied to an IP address to provide the network address portion of the IP address. For instance, an IP address might be 10.11.251.13 and the network that this IP address is assigned to might be 10.11.0.0 or 10.11.251.13 or 10.11.240.0. Here, we see how to apply the netmask, using the binary AND operation between the netmask and IP address. First, if the netmask and IP address are both in decimal, we have to convert them to binary. Notice that 255 = 11111111 and 0 = 00000000 making the netmask fairly easy to convert as it will usually consist of three total octets that are 11111111 and 00000000. The fourth octet, usually the second or third, may be a different value such as 11110000 or 11000000 or 11111100.