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Troubleshooting tips for VDI deployments

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Troubleshooting virtual desktop connectivity issues

Users occasionally have trouble connecting to their virtual desktops. These steps in the process of elimination can help troubleshoot network problems as quickly as possible.

Troubleshooting virtual desktop network connectivity can be tedious because of all the variables, but the job is a lot easier if you use a process of elimination to rule out as many potential problems as possible upfront.

Here are some basic techniques for troubleshooting network connectivity within virtual desktop infrastructures (VDI).

Narrow down the problem
When troubleshooting a connectivity problem, the first thing I like to do is eliminate as many potential causes as possible. The easiest way to do this is with a laptop or a netbook that is known to work perfectly. Remove the patch cable from the user's desktop, plug it into your laptop, and see if you can access the virtual desktop.

If your laptop can access the virtual desktop, you have just narrowed down the list of possible causes for the user's problem. Specifically, you confirmed that the user's patch cable is good, that the switch port to which the user is connected is good and that the various VDI-related server components are functioning. (Of course, if they weren't, you would probably be getting calls from multiple users.)

On the other hand, if your laptop isn't able to establish a virtual desktop session, something is wrong with the physical network hardware or with your network servers. Assuming that the phones aren't ringing off the hook, you can probably eliminate the VDI servers as part of the problem.

In any case, if you eliminate the user's physical desktop as the problem, you won't have to waste time troubleshooting it.

Pinpoint computer network, desktop connectivity issues
If you determine that the issue is related to your network hardware rather than to the user's physical desktop, test the user's patch cable, because patch cables go bad all the time. The reason? Patch cables are usually under the user's desk and tend to take a lot of abuse.

To test the patch cable, you can use a cable tester or just replace the cable and see what happens. My experience has been that a cable tester usually yields faster results.

If the patch cable is proven to be good, the next thing I recommend testing is the switch port that the user's connection is plugged into. I find that the wiring between the network jack and the switch rarely goes bad. However, I have definitely seen my share of bad switch ports. As such, try moving the user's connection to another switch port to see if that corrects the problem.

If you determine that the network infrastructure is good and that the problem is related to the user's physical desktop, the techniques you use next will vary depending on whether the machine is a PC or a thin client.

One of the best tools for troubleshooting PCs is the ping command. I usually start by pinging either the loopback address (127.0.0.1) or the computer's NetBIOS name. This ping test almost always works. If it doesn't, there is a problem with the physical desktop's operating system. It's usually related to a corrupted TCP/IP stack or a damaged network interface card (NIC) driver.

Assuming the loopback ping test works, try pinging a few critical IP addresses. For instance, you might ping the default gateway address as well as the domain name server’s (DNS's) IP address. If these pings fail, the problem is with connectivity or a driver. Since the network cabling and switch port have already been verified as functional, you could have a bad network card or a bad driver for the network card.

If these ping tests succeed, try pinging your DNS, domain controllers and maybe a few other key servers. This time, however, use the server's NetBIOS names rather than the IP address. This test will verify that your DNS is able to resolve the server names correctly. Keep in mind that this test will fail if a firewall is blocking Internet Control Message Protocol (ICMP) traffic.

If ICMP packets are blocked, then try pinging various websites (ping "www.sitename.com"). Most Web servers block ICMP (ping) traffic, but ESPN's site is great for testing connectivity because it allows its Web servers to be pinged. This will allow you to confirm connectivity from the desktop to the outside world.

If this type of ping succeeds, you have verified that the workstation’s connectivity is good and that DNS name resolution is working properly. It is safe to assume that the workstation has no problems with network connectivity.

It is therefore time to see if an infrastructure problem is preventing the user from establishing a virtual desktop session. For instance, you may find that the user already has a session and is for some reason unable to connect to it.

To further troubleshoot the problem, try logging in from the user's PC or having the user try logging in on a different PC. This won't fix the problem, but it will tell you whether the problem is related to the physical workstation itself or to the user's account. This knowledge should make it easier to troubleshoot the problem.

This was first published in January 2011

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Troubleshooting tips for VDI deployments

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