Diagnose And Repair SOHO networks

In this Recipe, I'll show you how to easily diagnose and repair the most common peer-to-peer networking issues with today's most popular consumer-based OSes from Microsoft.

As PCs continue to get more powerful and less expensive, a growing number of affluent households have more than one PC. Combine that with the proliferation of affordable broadband Internet and inexpensive wireless routers (which enable PCs to share an Internet connection, files, and printers), and system builders are looking at a new and growing market.

In fact, many computer technicians are being called out to install or repair small office, home office (SOHO) networks. With so many people receiving computers or networking equipment this past holiday season, 2005 is sure to become a record year for technicians to provide SOHO network repair. Learning how to diagnose and repair these small networks is a solid investment.

For this Recipe, I'm making the following assumptions:

Important: Using a crossover cable to connect two computers together is not recommended! Crossover cables exist for the sole purpose of connecting one hub/switch/router to another hub/switch/router. All other uses are not recommended. More details can be found on the Linksys Knowledge Base.

Four Things to Do Before You Begin Diagnosing

1. If any firewalls are installed on any of the PCs, uninstall them. This includes Zone Alarm, Sygate, Kerio, Norton Internet Security, Zero Knowledge Freedom, Cisco VPN Client, F-Secure, McAfee Firewall, Trend Micro, etc. In many cases, disabling the firewall is not enough; you have to actually uninstall it. Do not install or re-install the firewall until after you have the network functioning properly.

2. Ensure that the lights on the hub/switch/router are on for each port that a PC is plugged in to. Also make sure that the lights are on for the Ethernet jack located in the back of the PC. If the lights are not on, try resetting the router, different Ethernet cables, and different ports on the hub/switch/router. Be aware that some routers and broadband modems may have pause buttons. If a pause button does exist, press it to un-pause the router.3. If the problematic PC is wireless, be sure to disable all wireless security, including WEP (wired equivalent privacy) and MAC (media access control) filtering. Also, ensure that the SSID (service set identifier) is configured to broadcast on the wireless router/access point.

4. Regardless of how many computers you are trying to network together, start with just two. A bad network card, driver, cable, virus, or spyware on just one PC can jeopardize the integrity of an entire network. So turn off all but two PCs. Once you get these two working properly, then turn on one more and get it working. Then turn on the next, and so on, until you have all the PCs up and functioning properly on the network. The key is to start with just two PCs, then add the remainder one by one.

Are You Playing with a Full (Network) Deck?

Virtually all peer-to-peer home networking issues can be broken down into just three categories:

The first step in diagnosing any computer problem is ensuring you have the proper client, protocol, and service installed on the involved PCs. Regardless of which version of Windows your customers use, make sure they have Client for Microsoft Networks, TCP/IP, and File and Printer Sharing installed. You should remove all other clients, protocols, and services.Here's a screen shot of Windows XP Network properties with the recommended settings:

And here's Windows 98 Second Edition Network properties displayed with the recommended settings:

Also, ensure that NetBios is enabled over TCP/IP, and that your bindings are configured properly. A click-by-click walk-through is available on my Web site.If your customer is running Windows XP (Home or Professional), make sure they have no network bridges installed. If they do have bridges, delete them. In many cases, bridges are unneeded. In any event, setting up a bridge when a network isn't functioning properly is a lot like putting the proverbial cart before the horse. It won't help.

If any of the involved computers are running Windows Millennium (ME), be sure to download and install this patch from Microsoft. (Whether you think you need it or not, it won't hurt anything). If you wish to learn more about this WinME specific patch, it's all explained in detail here.

Getting Acquainted with the LAN

Windows includes a utility called IPCONFIG which offers a great amount of detail concerning a PC's network settings. It's the perfect place to start.

1. In Windows XP, click Start, click Run, type CMD and hit Enter.In Windows 98/Me, click Start, click Run, type COMMAND and hit Enter.

2. At the command prompt, type IPCONFIG /ALL and hit Enter.

What appears should look similar to the following example:

3. With Windows XP, take note of the Node Type. The error message "You might not have permission to use this network resource" will occur if the Node Type is set as "Peer-Peer." A Node Type of Mixed, Hybrid or Unknown is okay.4. To set the Node Type to Unknown (recommended), open the registry editor and go to: HKEY_LOCAL_MACHINE/System/CurrentControlSet/Services/Netbt/Parameters and delete these values if they're present: NodeType and DhcpNodeType. (You must reboot for changes to take effect).

5. If you have IP version 6 installed, your IPCONFIG screen may look similar to this:

6. If you see any Teredo Tunneling adapters, or an IP address that is separated by colons rather than periods (as shown in the image above), then you have TCP/IP version 6 installed. Most people do not need this protocol (at least not for a few years). To uninstall it, click Start, click Run, type CMD, and hit Enter. At the prompt type ipv6 uninstall, then hit Enter. A reboot will be required for the changes to take affect.

7. If you have a special need for IPv6, please temporarily uninstall it. Re-install it once your network is working properly.8. Take note of the IP Address. Every PC on the LAN should have the same IP address with the exception of the last number (octet). That last number must be different on each PC.

If your IP address starts with 169.254, then the PC was unable to automatically obtain an IP address; it has instead assigned itself an Automatic Private IP Address (APIPA). If there is no communication with a DHCP server on the network and no static IP address has been assigned, then the PC will assign itself an IP address in the 169.254.x.x range, as shown below. This may be normal or unexpected, depending upon how the network is configured.

PING!

The next diagnostic step is to determine whether each PC can see itself on the network. The PC refers to itself as the "localhost," and the IP address of every localhost is 127.0.0.1.1. On each PC, click Start, click Run. On XP: type CMD and hit Enter. On 98/Me, type COMMAND and then hit Enter.

2. At the prompt, type PING 127.0.0.1 and hit Enter. Here's the kind of screen that should result:

3. If the response to the Ping command times out, most likely a firewall is installed or a Microsoft service (in the case of WinXP) is not running. Some firewalls do not disable properly. Again, I recommend that you completely uninstall (rather than disable) all firewalls until your network is functioning properly. If a firewall does not uninstall successfully, reinstall the firewall and then try uninstalling it once more, preferably through Add/Remove Programs in the Control Panel. One exception: WinXP's built-in firewall can only be disabled; you cannot uninstall it.

4. If the PC can ping itself, the next step is to ping another PC by its IP address. If that fails, check the other PC for firewall software.5. Ping the other PC by its name. If you can ping successfully by IP address, but not by name, you most likely have a NetBIOS issue. Check to ensure that NetBIOS is enabled over TCP/IP on all PCs (described during the network setup instructions above). Also check that the "TCP/IP NetBIOS Helper" service is running on all XP PCs.

Inability to Access the Internet

If a PC can access other PCs on the LAN, but not the Internet, this is typically caused by a corrupt Winsock. The Winsock commonly becomes corrupt after Spyware infection or removal. The Microsoft testing procedure to determine if the Winsock is corrupt is quite complicated and time-consuming, therefore I recommend rebuilding it using one of the utilities listed below. These are much faster and won't cause any harm.

* For Windows 95, 98, 98se, & ME: LavaSoft

* For Windows XP: HomeTownOhioIf the PC can access some Web sites but not others, delete all temporary Internet files and try again. If the problem still exists, this is typically caused by an incorrect Maximum Transmission Unit (MTU) setting. Normally, this setting is set to 1500, but Internet connections that use PPPoE, which consumes 8 bytes for header information, need to have the MTU set to 1492 (or less) as a result. A great, free utility to adjust the MTU setting is Dr. TCP. To determine the optimal settings for Internet access on any PC, visit BroadbandReports.com and run the free Tweak Tester.

Inability to Browse the Local Network

On Windows 98/Me PCs: If clicking on the Network Neighborhood/Network Places icon results in an error or simply does not display other computers on the network, most likely the user is not logged in. Hitting Cancel at the logon screen (if one appears at boot up) can cause this behavior as well; so can an incorrect registry setting.

To fix, use the registry editor on the Win9x PC, and delete the following registry key: HKEY_LOCAL_MACHINE/Software/Microsoft/Windows/CurrentVersion/Network/Real Mode Net/AutoLogon. Re-boot for the changes to take effect. Remember to hit Enter or click OK when the logon screen appears.

Without getting into the complicated process of how the computers elect which PC becomes the "master browser," know that there can be only one. Also, some Win9x machines have difficulty negotiating with WinXP machines. This may be due to software, drivers or NIC hardware. But whatever the reason, you may need to disable the network browser entirely on the Win9x PCs.To determine how many PCs are acting as network browsers on the LAN, run the free Browstat program. Browstat is a free download from Microsoft that will run on XP/2000. You can find detailed information about it from Microsoft Support.

To determine the browser status of a Win9x PC, click Start, click Run, type COMMAND and hit Enter. At the prompt, type nbtstat -n and hit Enter. For more detailed reading on the Master Browser election process with Win9x, see this Microsoft TechNet page.

Inability to Access Network Resources

When trying to access a WinXP computer over the network, users may receive an error message that claims they do not have permission to access the resource. This may be caused by several things. XP Home users (as well as XP Pro users utilizing Simple File Sharing) need to ensure their network Guest account is enabled and has a blank password. This is not the same as the Guest account that exists in the accounts settings of the Control Panel.

1. To enable the network Guest account on XP Home and Pro, click Start, click Run, type: net user guest /active:yes, and hit Enter.2. Ensure there is no password for the Guest account: click Start, click Run, type: control userpasswords2, and hit Enter. Click once on Guest, click Reset Password, and then click OK without entering a new password.

3. Be aware that Windows XP, when installed on an NTFS disk partition and using simple file sharing, blocks network access to the Program Files and Windows directories as well as users folders within the Documents and Settings directory. This behavior is by design.

4. There are two registry keys to check on XP that have the potential to cause network headaches. The first is: HKEY_LOCAL_MACHINE/System/CurrentControlSet/Control/Lsa

5. Ensure that restrictanonymous is set to 0. Ignore the restrictanonymoussam entry that looks similar and may also appear.

6. Older versions of Norton Anti-Virus set a value for IRPStacksize in the registry that is too low for XP. In fact, XP doesn't even need this registry key. If you have it in your registry, thank Symantec and then delete it. If you determine that the XP registry has this unneeded entry, check this registry location:HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Services/Lanmanserver/Parameters. You can read more about this issue from Symantec and Microsoft.

If you're still having issues, a great place to start is Hans-Georg Michna's Windows XP Network Problem Solver site. You describe the scenario; the site provides numerous possible solutions.

Also, feel free to share any networking issues you have with us in the TechBuilder forums. We'll do what we can do to offer up a solution for you.

CAREY HOLZMAN is president of Discount Computer Repair in Glendale, Ariz., and the author of The Healthy PC: Preventative Care And Home Remedies For Your Computer (McGraw-Hill Osborne, 2003).

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