Chapter 8: Desktop Configuration Servers Overview TCP/IP is able to link the world together into a global Internet because it does not depend on any one physical network technology. It can run over the modem attached to a PC or over the fiber-optic network attached to a super computer. It does this by creating a logical network on top of the physical networks that is independent of the specific characteristic of any one network. However, this flexibility comes at the price of complexity. It is more difficult to configure a computer to run TCP/IP than it is to configure it for some other networks. You’re a technical person that’s why you run the network. Configuring TCP/IP may seem very simple to you, but it can be a daunting task for the average user setting up a PC. If your network is small, you can manually configure all of the desktop systems yourself. On a large network, manual configuration becomes an impossible task. Even on a small network, fixing the configuration every time a user upgrades is a thankless and boring job. The solution is to create a server that does this job for you, which is the topic of this chapter. Understanding Configuration Protocols Protocol developers have worked to reduce the burden of manual system configuring for a long time. Some of the documents that define the configuration protocols are more than 15 years old. Surprisingly, these protocols have come into widespread use only in the past few years. This is partly because the early users of the Internet were technical people who liked to configure their own systems, and partly because of the tremendous growth in the number of systems running TCP/IP that occurred at the end of the 1990s. Microsoft also deserves some credit for pushing hard to get people to use Dynamic Host Configuration Protocol (DHCP), which is the best of the configuration protocols. This section examines DHCP, as well as the other configuration protocols used to configure desktop systems. Bootstrap Protocol Bootstrap Protocol (BootP) was the first comprehensive configuration protocol. It can provide all of the information commonly used to configure TCP/IP from the client’s IP address to which print server the client should use. The BootP protocol is designed to deliver this information to the client, even though the client doesn’t have an IP address. Here’s how it works. The BootP client broadcasts a BOOTREQUEST packet to UDP port 67, using a special IP broadcast address of 255.255.255.255 that is called the limited broadcast address. The broadcast address assigned in Chapter 2, “The Network Interface,” with the ifconfig command was made up of the network address with a host field of all ones; for example, 172.16.55.255. Clearly, a BootP client that doesn’t know the network address couldn’t use such a broadcast address, which is why the limited broadcast address is used. Note Unless specially configured to do so, routers do not forward the limited broadcast address. For this reason, configuration servers are traditionally departmental servers, with one server placed on each subnet. Later in this chapter, we will see how relay servers can be used to support a centralized configuration server for organizations that prefer centralization over distributed departmental servers. 229
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