TCP/IP

Transmission Control Protocol (TCP) and Internet Protocol (IP), together referred to as TCP/IP, is a set of communications protocols used in the Internet and similar computer networks. The protocols specify how data should be formatted, addressed, transmitted, routed, and received.

The Internet Protocol defines an identifier, known as the IP address (or just IP in short), for each node on a network. The IP address of a node is used by the TCP/IP protocol to identify the source and destination nodes for data transfer. Hence IP addresses must be unique across nodes in a network and across interconnected networks.

For example, two office local area networks that do not ever intend to connect can use the same set of IP addresses within their respective networks. If they are intended to connect, they must use IP addresses that are unique across both networks. If a node is connected to the Internet, the IP address must be unique across the Internet.

Network administrators assign an IP address to each device connected to a network. Such assignments may be static or dynamic. In a static assignment, a device retains its IP as long as it is on the network, even if it shuts down and restarts or even temporarily leaves and rejoins the network. In a dynamic assignment, a device may be assigned a new IP every time it restarts or leaves and rejoins the network from a pool of IPs. In the case of the Internet, IP addresses are assigned by a global body so that every device on the Internet will have a unique IP address.

IP addresses have a specific structure. They are represented as four eight-digit binary numbers, separated by a dot. Each number can be one of 00000000 to 11111111 in binary or 0 to 255 in decimal. The complete IP address can therefore be anything between 0.0.0.0 and 255.255.255.255.

Some IP addresses are reserved for specific purposes on TCP/IP networks. For example: