In this chapter, our emphasis shifts from how TCP/IP functions to how it is configured. While Chapters 1-3 describe the TCP/IP protocols and how they work, now we begin to explore the network configuration process. The first step in this process is planning. Before configuring a host to run TCP/IP, you must have certain information. At the very least, every host must have a unique IP address and hostname. You should also decide on the items below before configuring a system:
If the system communicates with TCP/IP hosts that are not on its local network, a default gateway address may be needed. Alternatively, if a routing protocol is used on the network, each device needs to know that protocol.
To avoid broadcast problems, the broadcast address of every computer on a network must be the same.
If you're adding a system to an existing network, make sure you find out the answers from your network administrator before putting the system online. The network administrator is responsible for making and communicating decisions about overall network configuration. If you have an established TCP/IP network, you can skip several sections in this chapter, but you may still want to read about selecting hostnames, planning mail systems, and other topics that affect mature networks as much as they do new networks.
If you are creating a new TCP/IP network, you will have to make some basic decisions. Will the new network connect to the Internet? If it will, how is the connection to be made? How should the network number be chosen? How do I register a domain name? How do I choose hostnames? In the following sections, we cover the information you need to make these decisions.
First, you must decide whether or not your new network will be directly connected to the Internet. The Internet's administration makes a distinction between networks connected to the Internet and those that are not connected. A connected network is directly attached to the Internet and has full access to other networks on the Internet. A non-connected network is not directly attached to the Internet, and its access to Internet networks is limited. An example of a non-connected network is a TCP/IP network that attaches to the outside world via a mail gateway at America Online (AOL). Users on the network can send mail to Internet hosts but they cannot directly rlogin to one of them. 
 rlogin is covered in Chapter 9, Configuring Network Servers .
Many TCP/IP networks are not connected to the Internet. On these networks, TCP/IP is used for communication between the organization's various networks. Private networks that interconnect the various parts of an organization are often called enterprise networks. When those private networks use the information services applications that are built on top of TCP/IP, particularly Web servers and browsers, to distribute internal information, those networks are called intranets.
There are a few basic reasons why many sites do not connect to the Internet. One reason is security. Connecting to any network gives more people access to your system. Connecting to a global network with millions of users is enough to scare any security expert. There is no doubt about it: connecting to the Internet increases the security risks for your computer. Chapter 12, Network Security , covers some techniques for reducing this risk.
Cost versus benefit is another consideration. Many organizations do not see sufficient value in an Internet connection. For some organizations, low use or limited requirements, such as only needing email access, make the cost of an Internet connection exceed the benefit. For others, the primary reason for an Internet connection is to provide information about their products. It is not necessary to connect the entire enterprise network to the Internet to do this. It is often sufficient to connect a single Web server to the local Internet Service Provider (ISP) or to buy Web services from the ISP to provide information to your customers.
Other organizations consider an Internet connection an essential requirement. Educational and research institutions depend on the Internet as a source of information. Many companies use it as a means of delivering service and support to their customers.
You may have both types of networks: a "non-connected" enterprise network sitting behind a security firewall, and a small "connected" network that provides services to your external customers and proxy service for your internal users.
Unless you have carefully determined what your needs are and what an Internet connection will cost, you cannot know whether an Internet connection is right for your organization. Your local Internet service provider (ISP) can give you the various cost and performance alternatives. The next section offers ways to locate appropriate ISPs. Regardless of whether or not you decide to connect your network to the Internet, one thing is certain: you should build your enterprise network using the TCP/IP protocols.
Choosing an ISP for your network can be confusing. Currently more than 5,000 ISPs operate in the United States alone. No attempt is made to list them all here. Instead we provide pointers to where you can obtain information on ISPs via email, newsgroups, the Web, and in print.
Readers who want basic information about the Internet can start by reading a book about the Internet. My favorite is The Whole Internet Users' Guide and Catalog, by Ed Krol (O'Reilly & Associates). It provides a user-oriented focus on the Internet and a substantial list of ISPs. Another book that provides a business focus on "getting connected" is Getting Connected: Establishing a Presence on the Internet, by Kevin Dowd (O'Reilly & Associates).
If you can send email to the Internet, request information about the ISPs in your area by sending email to [email protected] with the words "MY AREA CODE =" followed by your area code in both the subject line and the body of the message. Here is an example for mail sent from a Solaris system to inquire for service providers for the 301 area code:
% Mail [email protected] Subject: MY AREA CODE = 301 MY AREA CODE = 301 ^D EOT
Use network news to obtain information about ISPs from the newsgroups alt.internet.services and alt.internet.services.wanted. Monitor alt.internet.services for announcements. Post a query to alt.internet.services.wanted asking if anyone knows of a good ISP in your area. Generally people in newsgroups have strong opinions and are willing to share them!
A good source of information about service providers is The List from Mecklermedia, which is accessible on the Web at http://thelist.iworld.com. The List contains information on thousands of ISPs. The information is sorted into country code and telephone area code lists to make it more useful.
Ask prospective ISPs about services as well as prices. Some ISPs specialize in providing low-cost service to home users. They emphasize price. However, if you are connecting a full network to the Internet, you may want an ISP that can provide network address, name service, Web services, and other features that your network might need.