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DHCP sure beats running around from machine to machine keying in fixed, or static, IP addresses and subnet masks in the TCP/IP control panel. Activate a Windows XP Professional machine as a DHCP client by clicking the Obtain An IP Address Automatically option on the General tab of the TCP/IP properties sheet. That's it!
Tip You can see the currently assigned IP address for your computer, and lease details for that address, by running the command-line program IPCONFIG (use the qualifier /ALL for the most complete display). You can also see a subset of address information by clicking the connection icon in the Network Connections folder and looking at the Details display at the bottom of the left window pane.
If you've set the automatic option, but no DHCP server is available, Windows XP uses a new feature called Automatic Private IP Addressing (APIPA). This feature makes the PC assign itself an IP address with a predefined format (169.254.x.x and a subnet mask of 255.255.0.0, which you should probably memorize for the exam).
Time Shaver The only way to turn APIPA off is to hack the Registry, but you don't need to know the specific key for the exam.
Instant Answer Windows XP PCs that have assigned themselves an IP address via Automatic Private IP Addressing can usually only communicate with other Windows XP, 2000, or 98 PCs on the same subnet that have done the same.
Instant Answer If no DHCP server exists on a subnet, Windows XP Professional machines can still use DHCP in two cases: If a router on the subnet supports DHCP forwarding (also called DHCP/BOOTP forwarding), or if a server (Windows 2002, 2000, or NT 4) on the subnet runs a service called DHCP Relay Agent. A machine running DHCP Relay Agent knows the IP address of the remote DHCP server, and can shuttle DHCP messages back and forth from subnet to subnet. You may see this tidbit crop up in exam questions having to do with Remote Installation Service (RIS), which only works if clients can 'see' a DHCP server in one fashion or another.
In the Windows NT networking scheme, every Windows computer has a NetBIOS name, or 'computer name,' which identifies it on a Microsoft-based network. In order for a network user to find your PC anywhere on a TCP/IP network by specifying your PC's NetBIOS name, the TCP/IP protocol must consult a lookup directory somewhere that correlates the NetBIOS name with an IP address.
That lookup is exactly what a WINS (Windows Internet Naming Service) server does. You set it up on the WINS tab of the Advanced TCP/IP Settings sheet (see Figure 6-8), which by the way you can configure differently for each different network adapter in the PC, if you have more than one. WINS is another program that can run on a Windows 2002, 2000, or NT Server in a TCP/IP network.
Figure 6-8: You can let DHCP provide WINS information, or specify it yourself.
There are two ways to set the address of a WINS server:
* Click the Default radio button.
Windows XP gets the address of a WINS server from the DHCP server.
* Click the Enable NetBIOS Over TCP/IP radio button and type the WINS server's IP address(es) yourself.
Instant Answer Without WINS, you can still browse the local subnetwork by using NetBIOS names, but you can't connect to Windows PCs on a remote subnetwork. The exam may include a question describing a situation where a user can see other PCs on the local subnet but can't find PCs on other subnets by using their NetBIOS names. The answer will probably reflect the likelihood that the user's WINS configuration isn't correct, or the WINS server is down, or NetBIOS over TCP/IP has been disabled on the client.
Instant Answer It's possible that the exam will ask you about LMHOSTS (refer to the related check box in Figure 6-8). This text file lives on the local PC and correlates NetBIOS names with IP addresses. Because administrators must maintain LMHOSTS manually every time an IP address change or a computer name change occurs on the network, LMHOSTS is an awful pain. Just remember that with WINS, you don't need LMHOSTS anymore. In fact, with DNS, one day you won't need WINS anymore, either, as I explain in the following section.
Yet another way of accessing computers on a TCP/IP network is by domain name (also called host name). You're already familiar with domain names such as www.dummies.com. A TCP/IP network doesn't have to use domain names, but doing so is often very convenient; for example, in a company-wide intranet. Here again, some facility must exist for domain names to be matched up with IP addresses. The typical facility is a DNS server, where DNS is short for Domain Naming Service (or, sometimes, Domain Naming System). Windows XP and 2000 networks rely heavily on DNS, not least for the new Active Directory service.
The DNS service itself only runs on Windows 2002 or 2000 Server, but you must know how to configure a Windows XP Professional machine to locate a DNS server on the network. The usual approach is to leave the Obtain DNS Server Address Automatically radio button selected on the TCP/IP properties sheet (refer to Figure 6-6) for the connection of interest. (This method uses DHCP to get the DNS server address or addresses - see earlier in this chapter.) Otherwise, you can click Use The Following DNS Server Addresses and type in a main and alternate IP address for the DNS server(s) on your network.