Troubleshooting Networks – CompTIA A+ 220-1001 – 5.7

| March 26, 2019


We rely on our wired and wireless networks for almost every aspect of modern computing. In this video, you’ll learn how to troubleshoot operating system network issues, intermittent connectivity, wireless interference, and more.

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If you’re connected to a wired network and you have no connectivity, make sure the cable is connected. And then look for a link light. This will tell you that you’re connected to a switch that is on the other end of that cable.

If you do have a link light, you can try to ping the loopback interface that’s on your computer. That interface is 127.0.0.1. This will at least tell you if the protocol stack that’s in your operating system is working properly, even if your network connection is not

The next logical step when troubleshooting this type of issue is to then ping your local IP address. If you’re on Windows, you can perform an ipconfig, find your IP address, and try pinging that address. That will at least tell you if the local configuration and the ethernet adapter that’s in your computer is working as expected.

The next logical step is to ping something that’s outside of our computer. And a device that should always be there is your default gateway. The default gateway IP address is also provided in ipconfig. So try pinging that address to see if you’re able to communicate across the network.

And if your default gateway is responding, you can try pinging something outside of your local network. A good example is the Google DNS IP address. Try pinging 8.8.8.8 and see if you’re able to ping out to the internet.

If you have not configured a static IP address on your computer and you turn on your computer and it’s not able to find a DHCP server, then it will automatically assign itself an APIPA address. The Internet Engineering Task Force has allocated a range of addresses to be used for these APIPA addresses. So the range is 169.254.1.0 through 169.254.254.255. The IP address ranges starting with 169.254.0 and 169.254.255 have been defined as reserved addresses. So those ranges will not be assigned to individual workstations.

When your computer is trying to assign itself an APIPA address, it chooses one of the IP addresses in this range. It then sends an ARP message, which is an Address Resolution Protocol, to see if any other devices on your network may have that IP address. And if nobody responds to the ARP, it assigns that IP address to the workstation.

And now your device is assigned an APIPA address that is somewhere in that range. If you were to look at your ipconfig, you’d be able to look at the local IP addresses. And if your IP address starts with 169.254, then you’ve been assigned an APIPA address.

There are many different kinds of resources on your local network that you may need to troubleshoot. For example, if you’re troubleshooting access to a Windows share and you’re not able to access that share, it could be because the server itself is currently unavailable. Or the server might be available, but someone may have modified your permissions to be able to access that share.

Another important thing to consider is that our computer is able to find that server using the domain name system, or DNS. If there’s problems with DNS, then we’re going to have problems connecting to the server that provides that share.

Connecting to a printer is very similar to connecting to a share. If someone has turned off their computer or the printer is unavailable, we may get a message saying that we’re not able to print to that device. And if somebody has changed the permissions to that printer, you may no longer be able to print because those security settings have been modified.

If you’re not able to access your email, there could be a single server or a cluster of servers that might be having problems. This may be related to the servers themselves. Or it may be related to the path in the network that’s used to be able to access those servers.

If you are having problems accessing different resources on the network, you may want to check the system tray in Windows. It may tell you that you’re having limited or no connectivity. Or it may say no internet access. You should check your local IP address and see if it’s an address that’s able to communicate to the internet or if for some reason you may have been assigned an APIPA address. If the DHCP server is working properly and you were assigned a DHCP address, then you can try the different pings to your local IP address, your default gateway, and then outside your local network to see exactly where along the line you’re having the communication problem.

Another challenging network issue to troubleshoot is one where the network is working fine and then suddenly, it’s not working at all. And then perhaps we have access again on the network. This intermittent access can be a challenge to troubleshoot. But there are a few things we can look at.

For example, let’s check the system tray and see what the icon shows for connectivity to the network. If we have a broken LAN icon in that system tray, then we have a loss of signal. And we may want to check the cabling that we use to connect to the network.

If our cable checks out OK, then we may want to look at the network interface card that’s in our computer to make sure that it’s working properly. If our cabling and our local device are working properly, we may want to check the infrastructure equipment that we’re using for our wired or our wireless network. We may have a switch or a wireless access point that is randomly rebooting and causing us to have intermittent connectivity to the network.

There might also be cases where we have two devices that are trying to share the same IP address. This IP address conflict is usually something that doesn’t occur if you have DHCP. But if you have some devices that are statically assigned and some devices that are DHCP-assigned, you may run into this conflict.

Fortunately, Windows and most operating systems will identify if someone else is on the network using that IP address before you actually are using it on your local workstation. If that is the case, Windows will display a message saying there is an IP address conflict with another system on the network. And you’ll need to find a different IP address to assign to your local workstation.

If for some reason you’re able to get the same IP address on two workstations on the same network, you’ll find that the devices work intermittently. One device will work during certain times and the other device during the other. Once you identify the two devices that have the IP address conflict and you’re able to resolve that, you can reboot or reset the NIC in one of the devices to restart the DHCP process.

Another networking problem that can be very difficult to troubleshoot is the network is slow. This might be because the infrastructure devices themselves are overwhelmed. If you have an older router or an older switch and it’s not able to handle the load, then you’ll certainly have some slowdowns in performance.

Another quick check when your network is performing slowly is to check the speed and the duplex of your local interface. You may find that you’re running at 100 megabits instead of gigabit. Or you may be set to half duplex instead of full duplex.

You also don’t want to discount any physical level problems. You may have a bad network interface card or a bad cable. And sometimes it’s malware that causes these slowdown problems in our operating systems and our networks.

Wireless networks can be even more difficult to troubleshoot because there are more things that can go wrong. For example, you could have interference from a third-party device that is using the same frequencies that we are using on our wireless network. You might also run into issues with signal strength. You want to be able to look at the transmitting signal from your access points, look at the transmitting antenna, and look at how the receiving antenna is being used on your local workstation.

You also want to make sure that you’re on the same channel as your access point. The access point is usually setting this channel information automatically. And the workstations are matching the access point. But if you’re setting those channels manually on your workstation, you want to be sure they’re matching the same channel that’s on the access point.

Our wireless signals tend to bounce off objects that are around us. And older access points may not be able to handle this multi-path interference when it’s received at the access point. You might also want to see where the access point is physically located. This might be an opportunity to move the access point closer to the users to improve overall performance.

Getting the best possible wireless signal can be a challenge in any environment. There are a number of devices that can create wireless signal interference, such as fluorescent lights, microwave ovens, cordless telephones, and high power sources such as transformers and generators. We also have the challenge of the unpredictable interference, such as third parties in a multi-tenant building.

Some of the troubleshooting tools you may want to use will be able to show you signal strength. You can sometimes see this in Performance Monitor in Windows. Or you might want to use a third-party tool to be able to map this information over an extended period of time.

If you bring up a list of all of the wireless networks in your area, you may find that your particular network is not appearing. There may be a couple of reasons why that might be happening. One of those reasons might be that your access point is too far away. You can see all of the local access points. But the signal from your access point is not making it to your workstation.

Or you may have configured your access point to intentionally not show itself in this list of access points. This is called a disabling of SSID advertisements. And if you’ve disabled those advertisements, they will never appear in that list of available networks.

Your wireless network is still available, of course. But you’ll have to manually configure your system to be able to connect to it. It’s not going to appear in a list of available wireless networks. But you’ll still be able to type in the SSID manually and connect to your wireless network.

Category: CompTIA A+ 220-1001

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