IP Addressing

IP addresses are 32-bit binary numbers. Each 32-bit IP address consists of two sub-addresses, one identifying the network and the other identifying the host to the network, with an imaginary boundary separating the two.

The location of the boundary between the network and host portions of an IP address is determined through the use of a subnet mask. A subnet mask is another 32-bit binary number that acts like a filter when it is applied to the 32-bit IP address. By comparing a subnet mask with an IP address, systems determine which portion of the IP address relates to the network, and which portion relates to the host. Anywhere the subnet mask has a bit set to 1, the underlying bit in the IP address is part of the network address. Anywhere the subnet mask is set to 0, the related bit in the IP address is part of the host address.