To participate on the Internet, every workstation and server computer must have a unique FQDN, and this FQDN must be mapped to a unique IP address. If a computer is multihomed, meaning that it is associated with more one IP address, each of the computer's IP addresses also must be unique.
TCP/IP, the protocol used throughout the Internet, is a routeable protocol, meaning that data can be passed, or routed, from one TCP/IP network to another. The intermediary devices that connect networks, referred to as routers, use IP addresses, rather than friendly names such as www.microsoft.com. The IP addresses provide routers an efficient method for locating computers and for addressing messages (in the form of IP packets) between computers. Therefore every device attached to a TCP/IP network must be identified by a unique IP address.
An IP address is a structured 32-bit number divided into four numeric fields separated by the . character (the period, also referred to as a dot), for example 172.46.8.34. Each of the four numeric fields is a byte (8 bits) in length. Each field can represent some number between 0 and 255; 255 is the maximum value that can be expressed by using 8 bits.
The four fields of an IP address represent two pieces of information, the network ID and the host ID of a computer. The network ID identifies a physical network. All computers on the same physical network must have the same network ID, and the network ID must be unique throughout the Internet. The host ID identifies a workstation, server, router, or other TCP/IP device. Each computer connected to a TCP/IP network must have a host ID.
Your intranet network administrator or Internet service provider (ISP) must provide a host ID and network ID for each computer that connects to the network. This IP address can either be manually configured or dynamically assigned by using Dynamic Host Configuration Protocol (DHCP) servers.
To connect your intranet to the Internet, you can obtain an allocation of network IDs for your enterprise computers by contacting either your ISP or the following regional Internet Registries:
InterNIC, the regional Internet Registry for the United States. Contact InterNIC at http://www.internic.net/.
Reseaux IP Europeene (RIPE) NCC, the regional Internet Registry for Europe. Contact RIPE NCC at http://www.ripe.net/.
Asia-Pacific Network Information Center (AP-NIC), the regional Internet Registry for Asia-Pacific. Contact AP-NIC at http://www.apnic.net/.