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Internet Connection Sharing: Don't bother.  All versions of Windows released since Windows 98 SE include a feature called Internet Connection Sharing (ICS) that lets you share a dial-up, cable, or DSL Internet connection with multiple PCs.  Though it sounds good on paper, ICS can be difficult to configure and manage.

First of all, ICS requires that you designate one computer as the gateway PC through which all your Internet traffic passes, and this PC must be powered on for the other computers to connect to the Internet.  Second, unless you're sharing a dial-up connection, you'll need to install two network cards in the gateway: one that connects to the broadband modem and one that connects to your LAN.

In most cases, you'll be far better off with an Internet gateway router, such as those sold by D-Link and Linksys.  These devices provide a connection between your LAN and the Internet. They're inexpensive (they're available for as little as $49) and easy to install, and they use very little power.  Virtually all gateway routers use Network Address Translation, or NAT, to share your DSL or cable modem's single IP address with all the PCs on the LAN.  Better still, most routers include a firewall feature that helps protect your LAN from hackers and intruders.

Don't have a broadband connection?  In some cases a gateway device includes a serial port or an internal modem so that you can use it to share a dial-up or ISDN connection.  Some models include 802.11 wireless network access points; others have built-in print servers; and almost all include three- or four-port 10/100 Ethernet switches.

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Fix A Mangled IP Configuration.  In the days before Windows XP, a corrupted IP installation could often be fixed simply by removing and reinstalling TCP/IP.  In most cases, the IP-related files remained intact, but some related Registry keys would be corrupted beyond repair.

You can't uninstall TCP/IP in Windows XP, because there is no Uninstall button for this protocol.  According to Microsoft, that is because TCP/IP is an integral part of the operating system, and removing it would cause major problems.  You can, however, use the Windows XP command line utility NetShell to reset all IP-related Registry settings to their default values.  The result is a brand-new TCP/IP configuration.

The Netsh.exe program is located in the C:\Windows\System32 directory.  To use the program, enter the command "netsh int ip reset filename." You must specify a filename, such as Ipstuff.txt.  After Netsh .exe runs, the file will contain a detailed log of the Registry keys that were modified.

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Use The Alternate IP Configuration Feature.  If you routinely move your laptop between two locations, you should know about Windows XP's alternate IP configuration feature.  If one location (your office, for example) requires a fixed IP address configuration, you can specify the office IP address, gateway address, and DNS server address information in the Alternate Configuration tab of the TCP/IP Properties page.

When your computer starts, it automatically attempts to obtain an address from a DHCP server.  If no DHCP server is found, Windows uses the alternate IP address information.  If a DHCP server is found (as would happen on a home LAN with an Internet gateway device), the system uses the DHCP-provided address instead.

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Use Network Bridging.  Windows XP has a new feature called Network Bridge, which lets you connect disparate media types into one seamless LAN.  For example, if you have a network PC connected to a LAN, cable modem, or DSL modem via Ethernet, you can create a bridge between the Ethernet connection and your PC's FireWire connection.

When you connect a laptop to the desktop via FireWire, the Network Bridge provides an IP connection to the laptop, even though the laptop isn't connected directly into the network.  To create a bridge, select two connections in the Network Connections control panel, then right-click on them and select Bridge Connections.

If you are bridging an Ethernet connection to a FireWire connection, you must manually set the IP address information (including IP address, gateway address, and DNS server address) on the FireWire-connected laptop, even if the LAN is configured to assign IP addresses automatically using a DHCP server.  If you frequently connect the same laptop to the same desktop, you can use the alternate IP address configuration feature to set the IP address to use for the FireWire connection.

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Install NetBEUI For Compatibility With Older LANs.  Previous versions of Windows automatically installed Microsoft's NetBEUI protocol whenever you installed a LAN card.  Windows XP, however, doesn't do this.  If you want to share files and printers with older Windows systems that don't have IP installed, you'll need to install NetBEUI manually.

Although NetBEUI is not officially supported, the files needed to install it are on the Windows XP CD.  To install NetBEUI:
Browse to the Valueadd\MSFT\Net\NetBEUI folder on your Windows XP CD.
Copy Nbf.sys to the C:\Windows\System32\Drivers directory.
Copy Netnbf.inf to the Windows\Inf directory.

Once you've copied these files to the proper directories, you can add NetBEUI to most network connections using the Install... button on each connection's Network Connection Properties display.  Unfortunately, you can't install NetBEUI on a FireWire connection.

NetBEUI doesn't require any addressing, routing, or other configuration information, so it is very handy for file sharing between laptops.  If you have NetBEUI installed on two computers, you can simply connect them together (using an Ethernet hub or crossover cable) to share files and printers.

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Automatic Wireless Device Configuration.  Windows XP includes built-in drivers for several popular wireless LAN cards.  In most cases, you can simply pop in a wireless card and use it with no configuration changes.  But the generic Microsoft wireless LAN driver doesn't provide access to some manufacturer-specific features, like manual channel selection and proprietary authentication schemes.

If you need access to these features, you'll need to install the driver provided with your wireless card.  But be aware that if you install a manufacturer-specific driver, you may lose the ability to connect to any wireless LAN you may encounter.  Whereas Windows XP automatically connects to any new wireless LAN that it sees, some manufacturers' drivers don't let you do this without changing settings (usually the system-specific ID, or SSID) in the LAN card driver.

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Networking with FireWire.  Although FireWire was originally designed to connect high-speed peripherals such as hard drives and CD-ROM drives, it can also be used as a very fast (400-Mbps) way to network two PCs.  In fact, Windows XP automatically creates a network connection for FireWire adapters.  The connection appears in the Network Connections control panel as 1394 Connection, and it works much like any Ethernet connection.

Unlike USB (which requires a special crossover cable to connect two PCs together), a FireWire connection requires no special cables, hubs, or adapters.  Be aware that there are two types of FireWire connectors in common use.  The larger, six-pin connector is most often used for external hard drives, CD drives, and other AC-powered equipment, while the smaller four-pin connector is used on DV camcorders and small, portable equipment.  Be sure to get a cable with the appropriate connections.

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Use the Hosts, Luke!  Whenever your computer connects to a resource on the Internet, it uses a Domain Name System (DNS) server to convert the human-friendly host name (such as \\Mailserver) or URL (such as www.pcmag.com) into an IP address.  A little-known feature (lifted directly from Unix) in Windows 98 SE or later lets you keep a table of host names and IP addresses on your own computer.  If this file - called the Hosts file - is present, Windows uses the IP address from the file without consulting a DNS server.

The Windows Hosts file can be found in C:\Windows\System32\Drivers\.  (In Windows 98 SE, the Hosts file is located in \Windows\.)  The plain-text Hosts file contains one line for each entry.

Even if you haven't created the Hosts file, it's there - with one lonely entry that defines localhost.  (Localhost is an alias used for testing, and it always refers to, the IP standard loopback address.)

You can add your own entries to the Hosts file using any text editor, such as Notepad.  The first (and less useful) way you might use this is to add the names and IP addresses of commonly used Internet hosts, so that Windows does not have to look up the address each time it connects to a given host.  But most DNS lookups are so fast that you won't notice any performance increase.

The second, more useful way to use Hosts is to create a dead-end address, known as a hacker IP address, for ad servers or for Web sites that you want to block.  For example, the entry adserver.annoying.com tells Windows to use to connect to Adserver.annoying.com.  Since that address doesn't exist, you'll never see the ad.  You can use the Hosts file as a cheap and dirty content filter in the same way: Simply create an entry for each host you want to block, using the address

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Where'd that printer come from?  The Automatic Search for Network Printers and Folders may have been intended to make your life a little simpler.  But this time-saving feature can be a real annoyance if you work on a large LAN or move your laptop among several networks.

When your computer is connected to a LAN, this feature periodically polls the network to see whether any new printers or shared directories are available on the LAN.  When Windows XP detects a new shared directory, it automatically adds a shortcut icon to My Network Places.  Similarly, new printers are added to the Printers and Faxes folder.  This can be convenient on a small LAN with just a few shared folders and printers, but on larger LANs, where users don't want or need to see every shared resource, this feature can cause confusion.

Fortunately, the auto-search feature is easy to turn off.  Go to the Control Panel and open Folder Options.  Then click the View tab.  The first item in the Advanced settings area is Automatically search for network folders and printers.  Uncheck the check box to turn the feature off.

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Find your IP address.  To get basic information about your TCP/IP network connection, you can use the Winipcfg utility in Windows 98 and Me (Start | Run | winipcfg), or use Ipconfig/all from a command prompt if you're running Windows 2000 or XP.

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Snoop on snoopers.  Turnabout is fair play.  The built-in networking features in Windows XP make it easy for other users to connect to your PC to use shared files and printers.  Unfortunately, those features also make it easy for snoopers, hackers, and backdoor programs to compromise your system's security.

Your first line of defense should be a combination of a secure firewall and a good antivirus program.  But even with these security measures in place, Trojan horse programs, e-mail viruses, and other nasty code can still get past your defenses.

If you suspect that someone (or something) is accessing your PC over a network or the Internet, there's an easy way to tell.  The command line utility Netstat shows the status and address of every connection to your PC.  Open a command line window and type Netstat -a to see a complete list of all the open connections to and from your PC.

Don't panic if you see lots of connections; most of them are supposed to be there.  If you see a suspect item in the connections list, you can type Netstat -o to get the Windows process ID number for each connection.  You can then match up the process ID number with the list of running tasks from Task Manager to see which programs are using which connection.

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Net Diagnostics,  Hidden in Windows XP's System Information utility is a very good tool for getting a lot more information about what's going on.  Go to Start | All Programs | Accessories | System Tools | System Information.  Then choose Net Diagnostics from the Tools menu.  The program will ping your DNS servers, gateways, SMTP and POP3 mail servers, and proxies; test your modem and network adapters; and supply very detailed reports about your settings, as well as which tests passed and which failed.

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