IP ADDRESSING

Using Transmission Control Protocol/Internet Protocol (TCP/IP)  requires that an IP address be provided for each computer, either automatically by Microsoft Windows, dynamically through the Dynamic Host Configuration Protocol (DHCP) service, or statically by using an IP address that you have obtained from your internet service provider (ISP).

Each TCP/IP host in identified by a logical IP address. A unique IP address is required for each host and network component that communicates by using TCP/IP.

The IP address identifies a system’s location on the network in the same way that a street address identifies a house on a city block. Just as a street address must identify a unique residence, an IP address must be globally unique and have a uniform format.

Network ID

Each IP address defines the network ID and host ID. The network ID identifies the systems that are located on the same physical segment. All systems on the same physical segment must have the same network ID. The network ID must be unique to the internetwork.

Host ID

The host ID identifies a workstation, server, router, or other TCP/IP host within a segment. The address for each host must be unique to the network ID.      

Address Classes

The internet community has defined five IP address classes to accommodate networks of varying size. The class of address defines which bits are used for the network ID and which bits are used for the host ID. It also defines the possible number of networks and the number of hosts per network.

Class A

Class A addresses are assigned to network with a very large number of hosts. The high-order bit in a class A address is always set to zero. The next seven bits complete the network ID. The remaining 24 bits represent the host ID. This allows for 126 networks and approximately 17 million hosts per network.

Class B

Class B addresses are assigned to medium-sized to large-sized networks. The two high-order bits in a class B address always set to binary 1 0. The next 14 bits complete the network ID. The remaining 16 bits represent the host ID. This allows for 16,384 networks and approximately 65,000 hosts per network.

Class C

Class C addresses are used for small local area networks (LANs). The three high-order bits in a class C address are always set to binary 1 1 0. The next 21 bits complete the network ID. The remaining 8 bits represent the host ID. This allows for approximately 2 million networks and 254 hosts per network.