What is an 'IP address'?

An IP address is a unique identifying number for a computer or device on the Internet. It is written as four numbers between 0 and 255, each separated by periods. For example,

What is a 'network number'?
The range of IP addresses assigned to a particular network is called its network number. A typical network number is expressed as nnn.nnn.nnn.0 where the zero stands for "all the addresses from 1 to 255." The AOL network number is, which means AOL computers can be assigned numbers from to

What is a 'domain name'?
A domain name identifies one or more IP addresses. For example, the domain name aol.com represents the IP addresses for the AOL computers. Domain names are often used in URLs (such as www.aol.com), and in email addresses (such as webmaster@aol.com).

What is an 'ISP' or 'Internet Service Provider'?
An Internet Service Provider (such as America Online (AOL), CompuServe, or MediaOne) is a company that provides access to the Internet. The ISP typically gives users a software package, username, password, and access phone number. With a modem, users can then log on to the Internet and browse the World Wide Web and send and receive e-mail. ISPs can serve both individuals and large companies, providing a connection from the company's networks to the Internet.

What is a 'nameserver'?
A nameserver translates names from one form into another. For example, the Internet uses Domain Name Servers (DNSs) to translate domain names into IP adresses.

What is a 'Domain Name Server' or 'Domain Name System' (DNS)?
Domain Name System (or Service), is an Internet service that translates domain names into IP addresses. Because domain names use letters instead of numbers, they are easier for people to remember than IP addresses (instead of remembering, people can remember www.aol.com). The Internet however, really uses IP addresses. Therefore, every time you use a domain name, a DNS service must translate the name into the corresponding IP address.

What is 'reverse name lookup'?
Every computer on the Internet has a unique identifying number called an IP address. The AOL server can compare this number to a database of domain names and network numbers to determine who owns that number. We then issue a request to the nameserver on that network to identify the domain name of that specific computer. A request of this nature is called a "reverse name lookup" (RNL) and is a standard part of networking protocol.

What is 'web caching'?
Web cache engines store Web pages that are frequently requested by users. Users do not actually get Web pages directly from Web sites, but rather from the caching computer. Caching computers feed pages to users either from pages that have already been stored, or by accessing Web sites to retrieve new pages which are then passed on to the user.

Must I supply my network number?
If your network Domain Name Server can correctly resolve reverse name lookups, the network number is redundant and therefore unnecessary. However, many networks are unable to correctly resolve reverse name lookups, which makes it necessary to know the network number.

Is my network number the same as my IP address?
No. The network number covers all the computers on your 'subnet', possibly your entire organization. Your IP address is only one address among the many in use at your site.
Why may reverse name lookups not work?
RNL's may fail for a variety of reasons, including firewalls, caching, or poorly designed security policy on your network or at your ISP (Internet Service Provider). Lookups might fail also on a very overloaded network, but this would be temporary.

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