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An IP address is an identifier for a computer or device on a TCP/IP network. Networks using the TCP/IP protocol route messages based on the IP address of the destination. The format of an IP address is a 32-bit numeric address written as four numbers separated by full stops. Each number can be between zero and 255. Your IP address, shown above, is an example of this.

Within an isolated network, in other words one that isn't connected to the Internet or any other network, you can assign IP addresses at random as long as each one is unique. However, connecting a private network to the Internet requires using registered IP addresses (called Internet addresses) to avoid duplicates.

The four numbers in an IP address are used in different ways to identify a particular network and a host on that network. Four regional Internet registries -- ARIN, RIPE NCC, LACNIC and APNIC -- assign Internet addresses from the following three classes.

• Class A - supports 16 million hosts on each of 126 networks
• Class B - supports 65,000 hosts on each of 16,000 networks
• Class C - supports 254 hosts on each of 2 million networks

The number of unassigned Internet addresses is running out, so a new classless scheme called CIDR is gradually replacing the system based on classes A, B, and C and is tied to adoption of IPv6.

DNS is short for Domain Name System (or Service or Server), an Internet service that translates domain names into IP addresses. Because domain names are alphabetic, they're easier to remember. The Internet however, is really based on IP addresses. Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address. For example, the domain name www.samarind.co.uk translates to 212.159.9.131.

The DNS system is, in fact, its own network. If one DNS server doesn't know how to translate a particular domain name, it asks another one, and so on, until the correct IP address is returned.

WHOIS is an internet utility that returns information about a domain name or IP address. For example, if you enter a domain name such as www.samarind.co.uk, WHOIS will return the name and address of the domain's owner ie. Samarind Limited.