The Internet has become such an essential part of most people’s experience that it’s sometimes difficult to know where your own computer stops and the Internet begins. For most of us, it doesn’t matter if a particular resource is physically located on a local hard drive (one inside your PC or a network server) or a computer halfway around the world. Either way, it’s just a matter of keystrokes and mouse clicks to view it on the screen or listen to it through speakers plugged into your computer. Of course, this assumes that your connection to the Internet is working properly. If you can’t view web pages, send and receive e-mail, or use any other Internet services, there’s probably a problem somewhere between your com- puter and your Internet service provider’s (ISP) point of access to the Internet. That problem might be due to a configuration error in your own computer or in the router, modem, or other device that connects you to the ISP. It could even be a breakdown in your ISP’s equipment. On the other hand, there’s nothing you can do to break the Internet. You can be reasonably certain that the Internet itself meaning the set of backbone networks and exchange points that connect millions of smaller networks and individual computers to one another is still out there, no matter how severely your equipment is broken. The Internet was designed to route traffic around damaged links and interconnection points, so it’s likely that nothing short of simultaneous explosive charges in about a hundred separate locations around the world could completely shut it down.

Isolate the Problem

As with any computer problem, when you have an Internet connection problem, you must first find the problem before you can fix it. Is it in your computer? Is it in the local network that connects the computer to your ISP? Could it be in the telephone line or broadband connection to the ISP, or at the ISP itself? And once you have located the problem you need to determine the cause. The first thing to do when your Internet service fails is to locate the problem. It could be in your own computer or your local network, in the dis- tant computer that is providing the data you see on your screen, or someplace between you and the distant machine.

Follow the Signal The Internet is huge. It connects tens of millions of computers together. So it’s absolutely essential to have a system that provides a name and location for each of those computers. Therefore, every computer and every intermediate routing device has a unique identity called a numeric Internet Protocol (IP) address assigned to it. That identity is a set of four numbers, each within the range from 0 to 255. A typical numeric address might be 206.83.231.2 or 192.168.0.1. To find a connection problem, you must follow the signal as it passes through the Internet and identify the numeric addresses assigned to each device between your computer and your ISP’s access point. If you discover that the signal stops short of its intended destination, that stopping point is probably the source of the problem. More specifically, you will need the IP addresses for these devices:

Your own computer

The local network hub or router

The ISP’s gateway to the Internet

Your Computer

When you set up your Internet account with an ISP, the ISP will provide instructions for setting up your local connection. Your computer’s IP address is either assigned dynamically by your network (via DHCP), or it is set as a static address in the Internet Protocol (TCP/IP) Properties window. To view your computer’s IP address, download and install Microsoft’s graphic IP Configuration tool from www.microsoft.com/windows2000/ techinfo/reskit/tools/existing/wntipcfg-o.asp. You can also view the IP address by choosing Start Run, then entering CMD and typing ipconfig. (The graphic program was part of the Windows 2000 Resource Kit, but it also works with XP, and it’s more convenient than the command-line version.) The IP Configuration window shows the IP address, along with several other addresses related to your Internet connection. In addition to the IP address, the IP Configuration tool displays several other important addresses:

Adapter address The adapter address is a unique identification number assigned to the computer’s network interface adapter at the factory. It’s also known as the Media Access Control (MAC) address. Some wireless networks restrict access to network adapters with specific MAC addresses.

Subnet mask The subnet mask tells the network which number in the numeric address provides a unique identity for each device on the local network. The other numbers are the same for all devices.

Default gateway The default gateway is the address of the computer or router that con- nects the local network to the Internet. If your computer connects to the Internet through a dial-up telephone connection or directly to a cable or DSL modem, the IP address is assigned by the ISP’s wide area network (WAN). If the computer is part of a network, the network hub assigns the IP address. Some ISPs provide a dedicated IP address to each customer (known as a static IP address), while others auto- matically assign an address when you connect to the network (dynamic IP address). When you set up your account, your ISP will advise you about which IP address to use, or it will show you how to accept an automatic assignment.

The Local Network Hub or Router

If your computer shares its Internet connection with other machines by way of a local network, the network uses a router a device that transfers inbound and outbound data between the local network and the shared Internet con- nection. The router presents its own IP address to the Internet and manages the addresses of all the other devices on the local network. The router’s address is the IP address assigned by the ISP. The local router uses two sets of addresses: one for the local network and one for its connection to your ISP. The user guide or other instructions for your network router should include the local address. (If you don’t have a user guide for your router, check the manufacturer’s website.) Your ISP will assign an address for your Internet connection.

The ISP’s Gateway

Your ISP should have provided the address of its gateway to you, along with other configuration information when you set up your account. If you don’t have the address, call your ISP and ask for it.

Tracing the Network

Now that you know the IP addresses of your own computer, your network router, and your ISP’s gateway to the Internet, you can trace the network connection all the way from your desktop to the Internet. If you can connect to a particular point in the series of addresses, but not beyond that point, the device that fails to respond is probably the source of your problem. To view a detailed list of the computers and other devices in a network connection, use a traceroute program that shows the IP address of each device between your computer and a specified destination, along with the amount of time it took to receive a response and the name assigned to each device. Most of the information in a traceroute display is more valuable to net- work administrators who want to follow signals through the Internet than to individual users, but the first three or four lines of a typical report show the path through the local network and the ISP’s WAN. If the path stops after one of the local devices, look for a problem in the device that should be next on the list. Traceroute probably won’t show the names of the local devices, but the IP addresses should be enough to identify each local device. Windows XP includes a command-line traceroute program.

To run a trace, open a command window (Start Programs Accessories Command Prompt), and type tracert destination, using the domain name (the Internet address) in place of destination. For example, to trace a route to No Starch Press, enter tracert nostarch.com. If you prefer, you can use one of several free programs that convert the traceroute data to a graphic display. One of the best is HyperTrace from AnalogX (www.analogx.com/contents/download/network/htrace.htm). Others include 3D Traceroute (www.d3tr.de), Visual Trace Route (www.itlights.com/traceroute.html), PingPlotter (www.pingplotter.com), and WinMTR (http://winmtr.sourceforge.net). In these examples, the first two hops pass through the local router with IP address 192.168.0.1. From there it moves through the ISP’s Internet gate- way at 206.251.63.1 (not the real address) and on to the ISP’s network. The next two IP addresses are hidden for security reasons, but after that, the connection moves out to the Internet on the way to the BBC’s website in London.

If the trace fails to show the local devices, the problem is in your local network. Check the Network Properties settings in Windows to confirm that all of the addresses and other values are correct (see the next sections of this article for details). If the trace makes it through the local network but stops at the ISP, call your ISP’s support center and ask for assistance.

My Computer Can’t Find the Internet

Whenever you try to use a program that connects to another computer through the Internet, you should make the connection without any unusual interruptions. You might have to enter a password to gain access to your Internet account, but after you have convinced your own ISP that it knows who you are, everything else should be automatic. But sometimes you might see an error message that is a variation of “unable to connect.” Depending on the program and the type of connection, this message could be text in an Internet Explorer (or another browser) window or in a separate error window in another program. Several things can cause a failure to make an Internet connection:

Your computer’s network configuration settings are wrong or missing. A firewall or other security software is blocking the connection. The modem that dials the ISP is improperly configured. Someone else is using the telephone line connected to your dial-up modem. The local network router is improperly configured. The ISP’s network server has a problem. The server you are trying to reach is offline.

Does Your ISP Provide Its Own Software?

Many large ISPs, including AOL, MSN, and EarthLink, supply their own proprietary software that automatically configures Internet access through their networks and installs an additional layer of software that may or may not add value to a generic Internet connection. If you are using one of these services, it may not be possible to connect to the Internet or change your configuration without using the ISP’s software. For example, if you are an AOL subscriber, you should use the America Online Setup window to change your configuration, rather than using the Windows settings described in the rest of this article. If you are working with an ISP’s proprietary software, don’t try to second- guess the configuration by making changes to the Windows Network Config- uration settings. If you can’t find a solution to the problem within the ISP’s own software, call their support center for help.

Network Configuration Settings

The configuration settings that you entered when you set up your computer to connect to the Internet should not change unless somebody or some- thing changes them. But if any of the settings do change, the computer won’t connect, so it’s important to know where to find them and how to correct them. Your ISP has probably given you an information card or sheet with a list of IP addresses, telephone numbers, passwords, and other information that you should use to set up your account. Some large ISPs, including America Online, MSN, and EarthLink, also provide a CD with their proprietary soft- ware that might configure your system for you. This is important information to keep around. You should store the information and the CD (if there is one) with your other computer manuals. Here are the essential addresses you must use to set up an Internet connection: The computer’s IP address. The subnet mask (probably 255.255.255.0). The default gateway that provides the interface between your ISP’s wide area network (WAN) and the Internet. One or more domain name service servers (DNS servers) that the ISP uses to convert domain names (such as nostarch.com) to numeric IP addresses (such as 64.49.240.173). If you don’t specify a DNS server, the Internet won’t recognize your request to connect to a domain name.

Some systems assign these addresses automatically, while others use the same addresses for every connection. Your ISP will tell you which options apply to your account. If you are using just one computer with a direct Internet connection, either through a dial-up telephone line or a broadband modem, the computer will use the addresses supplied by the ISP. If your computer is part of a local network, the router uses the addresses assigned by the ISP, and the computer uses addresses assigned by the router. In other words, each device computer or router sends its addresses back to the next device up the line. Look in your router’s user manual or quick setup guide to find the configuration settings for both the router and the computers connected to it. If you can’t find them, check with the router’s maker; their tech support people get these questions a lot. To view your current network settings and change them if they are not correct, follow these steps:

1. From the Start menu, select Control Panel Network Connections (in the Windows XP menu) or Settings Network Connection (in the Classic Start menu).

2. Right-click the icon for the connection profile that you want to open.

3. Choose Properties from the pop-up menu.

4. If you’re looking at a dial-up connection, choose the Networking tab. If you are using a LAN or broadband connection, choose the General tab.

5. Select the Internet Protocol (TCP/IP) item from the list of services, and click the Properties button. You might have to scroll down the list to find the Internet Protocol item.

The Internet Protocol (TCP/IP) Properties window includes spaces for the IP addresses assigned to this computer and the domain name service (DNS) servers.

Troubleshooting a Dial-up Connection

The Properties window for a dial-up connection includes tabs that control the telephone number of the ISP’s host and the IP addresses that the system will use to establish your Internet connection. The General tab sets the telephone number and offers a link to the Modem Configuration window. If your ISP changes its telephone number, you can enter the new number here. Many ISPs have more than one local telephone number to spread the load among several trunk lines. Your ISP’s support center can give you a complete list of local numbers if it was not included with your startup package or if it wasn’t on the setup CD. If you add an alternate telephone number, you can also instruct Windows to dial that number if the main number is busy. To add additional numbers, click the Alternates button. The Networking tab controls the network protocols that connect your computer to the Internet. Once again, your ISP’s support center can tell you exactly how to configure these options.

Troubleshooting a Connection Through a Local Network DSL, cable, and other broadband Internet services are always connected to the ISP, so it’s not necessary to dial a telephone number when you want to use the Internet. However, you do have to configure the modem and router that transfer data between your computer (or local network) and the ISP’s WAN. The first places to look when you’re troubleshooting a broadband connection are the Network Properties window for the local area connection and the setup windows for your router and your modem. Just like every other device on your local network, the router and the modem have their own numeric IP addresses. The manuals for each device will include the default address for that device, and most devices allow you to change the address to a value that isn’t known to everyone who has a copy of the manual.

Your broadband modem probably uses a graphic configuration utility that you can reach through your web browser, but some older routers might use a command-line utility that exchanges commands and data with your computer through a serial port. To find the specific routine for your own equipment, look in the manual for each device or ask your ISP’s support center for help. Wireless base stations (access points) are similar to routers for the purpose of this discussion: If they’re not integrated with a router or a modem, they just add one more layer to the system. To use the graphic configuration utility for your modem or router, open your web browser and type the device’s numeric address in the address field. The configuration utility uses an access port on the router or modem that can only be reached from the local network, so it’s not possible for outsiders to change your configuration through the Internet. Most configuration utilities require a password; you can find the default password in the manual, or you can obtain it from the manufacturer’s website or tech support center. You might need to use a computer connected to a different network or use a modem connection to reach the website, if the router is not working. Every other user on your network can also find those default passwords, including people who have no business changing the device’s settings. Unless you trust everybody on the network to leave things alone (including your children if it’s a home network), you should change the default password. Other manufacturers organize their utility screens differently, but they all contain the same basic information. Confirm that the router’s settings match the settings for the individual computers on the LAN side and the settings assigned by the ISP or the next upstream device (such as a modem) on the WAN side. If any of these settings are incorrect, you won’t be able to connect to the Internet.

The Computer Can’t Find a Particular Website

When you enter an address into your web browser, you expect a page to appear on your screen. If the network returns some kind of “unable to connect” message instead of the information you wanted, there’s a problem somewhere in the chain of devices between your computer and the server that contains that web page.

The most likely causes of a connection failure include:

1. The address is not correct. Confirm that the name you typed into the Address field is correct and that all words are spelled correctly. Make sure that all punctuation marks or symbols (such as & signs or underscores) are correct.

2. The site you requested does not exist. Websites appear and disappear without warning, so it’s entirely possible that the one you wanted has closed down. If you’re attempting to reach the site through a Google search, you can often find a copy by choosing the Cached link in the item description.

3. The web server that contains the page you wanted is offline or over- loaded (because a lot of people are trying to reach it at the same time), or it has some other problem. If a traceroute (described earlier in this article) breaks off before the actual site you want, that’s a good indica- tion that the server is offline.

If you can reach other websites (or other Internet services) but not the one you want, the problem is located at the distant system rather than your own computer or network. When that happens, there’s not much you can do to fix the problem other than notify the owners of the site by telephone or by some other method that does not involve using the Internet (if their web- server is down, they might not have working e-mail either). If you can’t find an alternative site that can supply the same information, your only other option is to wait until the problem is solved.

Computer Connects When You Don’t Want It to Connect

The opposite problem a web page that you did not request spontaneously appears on your screen is probably the result of either a scheduled task in a program that automatically searches for updates, or a hijack program that is misdirecting your browser. The first category a page related to a program, such as an antivirus utility is generally a valuable service that you should allow to continue. But a hijack program that opens an unwanted web page is definitely something to eliminate. If scanning your computer with an antispyware program doesn’t get rid of the problem, run a web search on the name of the program or unwanted site as it appears in the title bar at the top of your web browser window. Within the first two pages of matching sites, you should find at least one website devoted to killing and removing the spyware that is causing the problem. In most cases, following that advice will solve your problem.

The Internet Disappears

Sometimes your Internet connection suddenly seems to stop working without any notice, or it doesn’t work after you have turned on the computer for the day. If you’re not able to open any web pages or download any files, check all of the cables between your computer (or your wireless access point) and the wall outlet that carries your telephone line, DSL connection, or cable modem signal. If you’re using a dial-up modem connection, make sure nobody else is using the same telephone line. Make sure the modem and router (and any other device between the computer and your Internet connection) are turned on and that the power cables are plugged into their respective outlets. If none of the cables have come loose and everything is turned on, turn off your com- puter and the modem or router, wait 30 seconds, and turn everything back on again. Sometimes that’s all you will need to get the computer back online again; it’s amazing how often some kind of completely random “bit rot” mysteriously changes a critical setting. If it’s not a local hardware problem, telephone your ISP’s support center and ask whether there has been a wider failure. Their technicians will either know about the problem already, or they will tell you how to run some tests to help them identify the cause.

Firewalls and Gateway Servers

Firewalls (which might be either hardware or software) are designed to thwart outside intruders’ attempts to introduce unwanted commands into a com- puter, and their attempts to possibly take control of it or steal data. They accomplish this by limiting access to software ports on your computer that are commonly used for standard applications like e-mail and web browsers. Firewall design is a compromise between convenience and security, so some firewall programs are more aggressive than others. Some firewalls won’t allow any program to connect to the Internet unless it’s on a list of acceptable programs. Well-behaved firewalls display a message asking if it’s okay to connect when you try to use an unknown program, but others simply block the connection without any notice. Therefore, it’s possible that a connection failure is nothing more than the firewall doing its job.

Each firewall is different, but most of them offer an easy way to temporarily turn off their blocking functions. If you suspect that your firewall is keeping another program from connecting, turn off the firewall and try to connect again. If the connection works without the firewall, look in the firewall’s manual or online help for instructions about adding the blocked program to the list of accepted connections. Don’t forget to turn the firewall back on when you’re done. Don’t be intimidated by an Internet problem just because it’s the Internet. Like electricity, water, telephone service, and other public utilities, the Internet works reliably almost all the time. When it doesn’t work, the problem is almost always limited to a small portion of the system. The Internet may be big and complicated, but it follows a set of well-defined rules that make troubleshooting relatively easy. If you apply a logical approach to locating the cause of a problem, you can almost always find a way to fix it.