This simple networking connectivity troubleshooting exercise can help you think more broadly the next time you encounter a similar issue.
The built-in troubleshooting features of Windows 7 can help you resolve most matters quickly. However, you’ll occasionally encounter other issues that can’t be so quickly or easily resolved.
Consider this: There’s a system that’s one of many running on a fairly complex small business network. The network has a single router and multiple network switches. When the OS starts, the computer is unable to connect to the network or to the Internet. The computer is running Windows 7 x64 and has a single 1.0Gbps network adapter.
The first step in troubleshooting any connectivity problem is always the same. Check the networking status. This is easy enough to do. Simply look to the system tray. Here, the Network icon in the system tray shows a warning sign. Clicking the Network icon and then clicking Open Network and Sharing Center reveals that this computer with a single network adapter thinks it’s on multiple networks.
What has happened here is at startup, the computer checked the networking configuration, found the adapter, but was unable to determine exactly how it was connected to the network. As a result, the computer has no network connectivity and no Internet connectivity whatsoever. Any ideas on what the problem is here? Here are some things to think about:
How would you go about troubleshooting and resolving the problem? Let’s dig deeper and take a look. This type of problem is not so much a problem as it is a puzzle waiting to be solved. So where to begin unraveling the puzzle?
Let’s start with “Check the obvious” and call that Step 1. The question we’re seeking to answer is whether this is just a quirk or a temporary hiccup. Also implied here is a check of the basics. That means checking the cables to ensure they’re connected in the right places.
So is this a quirk, a signal hiccup or a basic cable issue? This is easy enough to determine as well. If this was a problem with the connection between the switch into which the computer is plugged and the router, or between the router and the Internet, the problem would show in the Network and Sharing Center as a lack of connection between the network and the Internet.
Clicking the red X in the summary network map launches the built-in networking troubleshooter. The troubleshooter will try to connect to Microsoft to troubleshoot your Internet connection. When there’s a disconnect between a switch and a router, it’s largely indistinguishable from a TCP/IP configuration problem at this point.
When you proceed with automated troubleshooting, the networking troubleshooter checks mostly for configuration issues and won’t necessarily be able to tell you there’s a disconnect between the switch and the router. The troubleshooter performs the following checks in this order:
To see the detailed results of the automated troubleshooting, you need to click the View Detailed Information link it will provide. You’ll then be able to access the troubleshooting report. If this were a problem with the computer’s connection to the switch, the problem would show a red X between the specific computer and the Internet in the Network and Sharing Center.
Clicking the red X in the summary network map again launches the built-in networking troubleshooter. The troubleshooter would then quickly would tell you to plug an Ethernet cable into the computer, then click check to see if the problem is fixed.
Of course, you could’ve checked for the problem in the Network Connections window and you would’ve known the same thing. The local area connection failed because a cable was unplugged.
Whether the computer end or the switch end was disconnected, it only takes Windows 7 a few seconds to detect that you’ve reconnected the Ethernet cable. Windows 7 will then attempt to connect you to the LAN. If the computer is connected to a switch and not to the rest of the LAN and the Internet, Windows 7 likely will show that you’re connected to an Unidentified Network and you have no Internet access.
The problem the computer is experiencing here, however, is very different. The computer thinks it’s on multiple networks. It has no network connection and no Internet connection, even though the basic cabling is good. So is this just a quirk or hiccup? One way to check is to simply disable and then enable the network adapter.
This forces the computer to reevaluate the networking components and configuration. More important in this particular case, the problem appears to go away. The network connectivity returns and everything looks good. But is the problem really fixed? Not in this case. So as this particular problem isn’t a quirk or hiccup, let’s move on to Step 2.
Here you want to answer whether this is a basic hardware problem. You may have already answered this if you looked at the Network Connections page. If the active network adapter has an adverse status, such as Disabled or Network Cable Unplugged, it will show this and the corrective action is easy. You enable a disabled adapter, or plug a cable into one that has an unplugged cable.
What about the case where the Network Connections page is empty or doesn’t otherwise have a local area connection as it should? This does happen. You should then click Control Panel | Network and Internet | Network and Sharing Center | Change Adapter Settings, only to find no local area connection listed, even though you know the computer has a wired network adapter.
In this case, a quick check of Device Manager will tell you what’s going on. Device Manager is accessible from Computer Management. To start Computer Management, click Start, type compmgmt.msc in the Search box and press Enter.
In Computer Management, select Device Manager and then expand the Network Adapters node to check the status of the installed adapters. If you see a warning icon, the device has an error status that you can check by right-clicking the related entry and selecting Properties.
If the device isn’t listed at all, as would happen if the device were uninstalled, you can right-click the Network Adapters node and select Scan for Hardware Changes to have Windows check for available but not installed devices. Consider the following:
A device with a normal status likely doesn’t have a basic hardware problem. To troubleshoot this type of problem, find a test machine. Go into Device Manager, expand the Network Adapters node, right-click the adapter and then select Uninstall. After you uninstall the adapter on your test computer, you can work through Step 2 of this troubleshooting scenario and see if you can use the information provided to resolve the problem.
Clearly, there’s some type of problem going on preventing the computer from connecting to the network and the Internet properly. In Step 1, you checked the obvious. In Step 2, you checked the hardware. If you’re experienced at this sort of thing, all these related checks probably took you a minute or less.
Normally, this type of problem would be easy to resolve. However, this computer with a single network adapter thinks it’s on multiple networks. Therein lies the crux of the problem. What has happened here is at startup, the computer checked the networking configuration, found the adapter, but was unable to determine exactly how it was connected to the network. As a result, the computer has no network connectivity and no Internet connectivity whatsoever.
In Step 3, you’ll try to determine if this is a configuration problem. Often, the fastest way to check for a configuration problem is to use the Command Prompt. Display the networking configuration by entering ipconfig /all. In the output, check the IPv4 (and, if appropriate, IPv6) configuration. For IPv4, look specifically at the following:
The assigned values should be appropriate for the network to which the computer is connected. If Dynamic Host Configuration Protocol (DHCP) is enabled, then make sure the computer has connected to the appropriate DHCP server.
If the computer hasn’t connected to a DHCP server, it will have an IP address in the automatic private IP addressing (APIPA) range: 169.254.0.1 to 169.254.255.254. A computer with an APIPA likely can’t communicate appropriately on the network. As a result, Windows periodically checks for a DHCP server to become available.
If the computer looks like it has the appropriate network settings, try a ping or tracert to the default gateway. In some cases, a ping is blocked by firewall settings, but tracert should work. If a ping or tracert fails here, it likely indicates a connection problem between the computer and the default gateway or a problem with the default gateway itself. To resolve a connection problem, you’d check the cabling and switches between the computer and the default gateway.
To resolve a gateway problem, you’d need to look at the device itself to determine its status and configuration. Keep in mind, however, that you can’t connect to a nonexistent gateway. A computer configured on the network 192.168.27.x should have a default gateway of 192.168.27.1 in most cases. However, if the network settings are wrong and the computer is actually on the 192.168.12.x network pinging 192.168.27.1, it likely won’t return any results because the correct gateway IP address is most likely 192.168.12.1.
If the computer can access the default gateway, try a ping or tracert of a known Internet site. Again, in some cases, the firewall might block the ping, but the tracert should work. Failure of a ping or tracert here would indicate a problem with the Internet connection or Internet service. You’d need to slice and dice it a bit more to be sure. For example, if you can’t ping or tracert by site name, such as tracert www.yahoo.com, you should ensure this wasn’t a DNS problem.
To check this, you should ping or tracert an external site by its IP address. If you can get to the external site by its IP address, but not its fully qualified name, you likely have a DNS problem. Resolve the DNS problem by verifying the DNS server IP addresses and setting the server IP addresses as appropriate. You might also need to flush the DNS resolver cache. To resolve an Internet connection problem, check the cabling between your internal router and the device that routes to the Internet. You should also check the device status.
In this scenario, the computer has DHCP-assigned IP settings and was able to get those settings from the DHCP server. Because of this, checking the TCP/IP configuration at the command line seems to provide the correct settings.
If you thought the problem was related to the DHCP settings, you could perform a variety of troubleshooting tasks with Ipconfig at the command line. Ipconfig /release, Ipconfig /renew, Ipconfig /flushdns and Ipconfig /registerdns are all handy commands.
If you thought the problem was related to assigned settings, you could review the adapter settings by clicking Control Panel | Network and Internet | Network and Sharing Center | Change Adapter Settings.
Then on the Network Connections page, you’d right-click the appropriate adapter and then select Properties. In the Properties dialog box, select Internet Protocol Version 4 and click Properties. You can now review the IPv4 configuration.
One way to troubleshoot a networking problem at this stage is to manually assign IP settings that you know should work. If you’re able to manually assign settings and connect to the network and to the Internet, the problem likely is related to DHCP. Here are the likely suspects:
Any guesses as to what happens when you manually assign IP settings? Well, it does force the computer to modify its configuration. More importantly, in this particular case, the problem appears to go away. The network connectivity returns and everything looks good. Is everything really OK, though? Only you will know.