Automatically Configure TCPIP

Automatically Configure TCP/IP

Fortunately, you hardly ever have to actually configure TCP/IP properties for yourself. Instead, most network implementations today use a technology called Dynamic Host Configuration Protocol (DHCP), which automatically assigns IP address configuration information, including the subnet mask and (usually) default gateway. The process is as follows: your computer boots up, and as a part of XP initialization, the system contacts a DCHP server and requests an IP address. It does so because the TCP/IP Properties are configured by default to "Obtain an IP address automatically," as shown in Figure 9-4.

Figure 9-4. Obtaining an IP address automatically.

When this option is selected, your system is a DHCP client. Where is the DHCP server on your network? Well, it's probably your Internet Service Provider. If you have a persistent Internet connection, such as one from a cable or DSL connection, the ISP is your DHCP server. In other words, your Internet Service Provider typically assigns your TCP/IP address, and it could be a different address every time you reboot.

But DHCP servers can exist on other devices as well. If you're sharing out that same broadband connection with a router, your XP computer becomes a DHCP client of the router, and the router in turn is a DHCP client of the ISP.

What's a DNS Server?

DNS stands for the Domain Naming System, and it's the naming convention that allows you to type www.prenhall.com into a Web browser rather than 165.193.123.253 (go ahead; that's the real IP address of prenhall.com). In other words, it allows humans to remember text names instead of numbers. If the phone system were like this, you'd never have to remember anyone's phone number. You could just say "William Gates" into the phone, and a huge, centralized phone book would locate the number for you. (The phone system can't work like this because there are too many people named William Gates in the world.) A DNS server basically stores and manages a list. The list maps the names of computerslike www.prenhall.comto IP addresses. You type www.prenhall.com into the browser, and XP sends out a query to the configured DNS server. The query asks, "What's the IP address assigned for www.prenhall.com?" The DNS server consults its list (most DNS server can consult the lists on other DNS servers as well) and, if a match is found, returns the IP address for www.prenhall.com (165.193.123.253 in this case) to the XP system. Computers prefer numbers, so with this number now in hand, the XP system and the www.prenhall.com Web server can exchange information.