Accessing the Internet


If you are a user on a multiuser system or if your computer is part of a larger network at a company, an educational institution, or some other organization, you may already be connected to the Internet. If this is the case, you can access Internet services using the appropriate commands described later in this chapter and in Chapter 9. However, if you want to access the Internet from your own computer, you have two choices: You can connect to the Internet directly, or you can use a public-access provider. Directly connecting to the Internet is complicated and beyond the scope of this book. Unless you plan to become heavily involved with the Internet, a better option is to use one of the many public-access providers.

Using a Public-Access Provider

To use a public-access provider, you need to connect to a public-service provider, called an Internet service provider (ISP). ISPs generally charge a fee for using their system to access the Internet. These providers offer a wide range of Internet services. In many places you have several options for how you connect to the Internet. You can connect using a modem over a standard telephone line. You can also take advantage of a high-speed Internet connectivity option, including connections made using a cable modem over cable lines and connections made using a digital subscriber line (DSL) modem over regular telephone lines. If you select a connection using a modem over a regular telephone line, you should find a local (in the sense of a local phone call) Internet access provider or one with a toll-free number, to keep your phone bills low. You may want to select a provider that charges a flat monthly fee that allows use for a large block of hours per month rather than a usage-based fee, because it is very easy to find yourself connected to the Internet for hours at a time. If one or more high-speed connections are available at your location and you are willing to pay the extra cost, you will pay a flat monthly service fee that will provide you a permanent connection to the Internet. Check with your local cable company and DSL providers for details.

Internet Addresses

Each computer on the Internet has an official Internet address, known as an IP address, together with a name that uniquely identifies that computer. Because people prefer using names for computers, whereas networking software uses IP addresses, a way is needed to translate the name of a system to an Internet address. This mapping is provided by the Domain Name Service (DNS). When a program encounters the name of a computer, the program uses the DNS to translate this name into its IP address. See further discussion in this chapter, as well as in Chapter 17, for more information.

IP Addresses

Every computer on the Internet has an IP address that is made up of four integers between 1 and 254 (with 255 used in subnet masks that are used to separate host parts of an address into two or more subnets), separated by dots, such as 127.64.11.9. The first part of the address specifies a particular network that is part of the Internet, and the second part of the address specifies a particular host on that network. The rules for assigning these numbers lie beyond the scope of this book.

Internet System Names

Names of systems on the Internet (known as fulty qualified domain names) consist of alphanumeric strings separated by dots. For example, zeus.cs.unj.edu is the full Internet name of a particular host; here zeus in the name of the system, cs represents the group of all systems in the computer science department, unj contains all systems at the (fictional) University of New Jersey, and edu contains all systems at educational institutions in the United States. Here, edu is one of several possible top-level domains.

There are two varieties of top-level domains. The first, organizational domains are designed to be used inside the United States. A top-level domain in the United States indicates the type of organization that owns the computer. For example, the domain edu is used for computers at educational institutions. It is important to note that organizational domains were devised before the Internet became an international network. This has led to a different type of top-level domain being used outside of the United States. Instead of using the type of organization, computers on the Internet outside of the United States use geographical top-level domains where two letters are used to represent each country of the world. For example, the domain nz represents the top-level domain of computers in New Zealand.

Domain Name Service (DNS)

As mentioned previously, a machine node name is linked to a particular IP address through the DNS service. To use this service, you must register your machine with a server that runs the translation software, called a Domain Name Server. The only two pieces of information that are needed are the machine node name, or DNS name (such as stu.att.com), and the current IP address (such as 135.19.47.203). These two items are stored in a DNS table. Once you are registered, all users can access your machine via its DNS name. This capability is especially useful when your internal IP network changes its addresses frequently. Your local DNS administrator can change the IP address in the DNS table to point to the new address without requiring the people that want to reach you to do anything, since the node (DNS) name that they use to contact you will remain the same. We will discuss DNS in more detail in Chapter 17.




UNIX. The Complete Reference
UNIX: The Complete Reference, Second Edition (Complete Reference Series)
ISBN: 0072263369
EAN: 2147483647
Year: 2006
Pages: 316

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