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Appendix C: IP Addresses & Hostnames

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Appendix B: WHOIS Servers

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An IP (Internet Protocol) address is a numerical sequence that uniquely identify a computer, or other networked device, on a network such as the Internet. To be able to use the Internet, your computer needs an IP address so that network traffic can be directed to and from it.

When you log on to the Internet, your Internet Service Provider (ISP) typically assigns you an IP address for your current session. If you use a dial-up, you usually receive a different address each time you connect. If you connect to the Internet from a local-area network, like you might at work, or through a cable modem or DSL line, you might have an IP address permanently assigned to your computer.

Anytime you send an e-mail, access a Web page, or try to send or gather other information to or from the Internet, your Internet application communicates with a server via its IP address. IP addresses are usually formatted by means of four numbers from 0 to 255, separated by dots. A typical IP address might be "209.94.162.45".

Since it is difficult to remember arbitrary strings of numbers, and an IP address for a given computer can frequently change, textual "hostnames" are used in place of numeric addresses. Hostnames are used to make addresses easier to remember, and to continue to identify a specific computer even when its IP address changes. DNS (Domain Name System) is the Internet function that provides "hostname resolution", which translates textual hostnames into numeric IP addresses.

The Domain Name System is what enables you to type in names (such as "www.freshsoftware.com") instead of numerical IP addresses. When DNS translates hostnames into their numerical counterpart, the process is usually transparent to the end user. When an Internet application encounters a textual hostname, it sends a request to a DNS server. The DNS server will then respond with the IP address associated with the textual hostname, or it will signal an error if it cannot find an associated address.

For more information: The In’s and Out’s of DNS