In this chapter, our emphasis shifts from how TCP/IP functions to how it is configured. While Chapters Chapter 1, " Overview of TCP/IP" through Chapter 3, "Network Services" described 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 resolve the following issues 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 resolve hostnames into IP addresses, each host needs to know the addresses of the domain name servers.
Hosts using the domain name system must know their correct domain name.
To communicate properly, each system on a network must use the same subnet mask.
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 so, how will the connection 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 your new network will be fully connected to the Internet. A connected network is directly attached to the Internet and is fully accessible 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 network address translation (NAT) box or a proxy server. Users on the non-connected network can access remote Internet hosts, but remote users cannot directly access hosts on the non-connected network. Because non-connected networks do not provide services to the outside world, they are also known as private 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 fully 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 network. Chapter 12, "Network Security " covers some techniques for reducing this risk.
Cost is another consideration. Many organizations do not see sufficient value in a full Internet connection for every desktop. For some organizations, low use or limited requirements, such as needing only email access, make the cost of connecting the entire network to the Internet 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 work with a web hosting company 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, and 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 connecting your entire network to the Internet is right for your organization. Your local ISPs can give you the various cost and performance alternatives. Ask them 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 addresses, name service, web hosting, and other features that your network might need.
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