Troubleshooting tips for VDI deployments
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Remote desktop connectivity is usually reliable, but things can -- and sometimes do -- go wrong.
There are five common remote desktop connection problems that come up: network failure, firewall problems, Secure Sockets Layer (SSL) certificate issues, authentication, and capacity limitations. You can prevent and solve these problems easily with a few pointers on remote desktop troubleshooting.
One of the most common remote desktop issues is a failure of the underlying network. To check for connectivity, try plugging a laptop into the network port from which the user is trying to connect, and then use the Ping or Tracert command to see if it's connected to the host server or connection broker. Keep in mind that testing remote desktop connectivity this way will only work if you allow ICMP packets through your network firewalls.
If the problematic user is connecting remotely through a virtual private network (VPN) or Terminal Services Gateway, the remote desktop might not be working because of a problem with the user's machine, the VPN or gateway, or your remote desktop infrastructure. With these types of remote desktop issues, you’ll have to use process of elimination to diagnose the problem. For example, try connecting to the VPN using a properly configured client computer and a reliable user account to see if you can establish remote desktop connectivity.
It's easy to dismiss the notion that a firewall could contribute to a remote desktop not working, but it's actually quite common. To avoid problems with the firewall, ensure that the port your remote desktop software uses is open on all firewalls between the client computers and the server they connect to.
You may need to configure multiple firewalls. For example, the client and the server may both run the Windows Firewall, or there may be multiple hardware firewalls between the two systems. Plus, the port number that should be open on the firewalls differs from one virtual desktop infrastructure (VDI) product to the next. Remote Desktop Protocol-based tools use port 3389 by default.
SSL certificate issues
Security certificates can also cause remote desktop connectivity problems. Many VDI products use SSL encryption for users who access VDI sessions outside the network perimeter. But SSL encryption requires the use of certificates, which creates two problems that can cause a remote desktop to not work.
First, if the remote desktops are going to connect properly, client computers must trust the certificate authority that issued the certificate. This isn't usually a problem for organizations that purchase certificates from large, well-known authorities, but clients won't always trust certificates that an organization generates in-house. Use a reliable certificate authority to ensure that clients establish remote desktop connectivity.
The client must also be able to verify the certificate that the server is using. The verification process can break down if the certificate has expired, or if the name on the certificate doesn't match the name of the server that's using it, so make sure your certificates are up to date.
In Windows Server 2008 R2, Microsoft's Remote Desktop Services is designed to use a security feature called Network Level Authentication. The basic idea is that the session host must authenticate the user before it can create a session. Not only does network-level authentication improve security, but it also helps decrease the amount of VDI resources the session uses.
Network-level authentication can prevent remote desktop connection problems later in the session, but not all remote desktop clients support it. If you use Microsoft clients, you can determine whether they support network-level authentication by clicking the feature's icon in the upper left corner of the Remote Desktop Connection menu and choosing About from the resulting menu. The client will explicitly state if it supports Microsoft's Network Level Authentication.
If you don't see the message that your client supports it, you can either upgrade the client component or disable the requirement for network-level authentication on your VDI servers. Keep in mind that Network Level Authentication is also sometimes enabled through Group Policy settings.
Finally, you could experience remote desktop connectivity issues if you exceed the infrastructure's capacity. One thing that might cause remote desktops to not be working properly is if you've run out of virtual desktops or VDI licenses. Some VDI implementations also refuse client connections if the server is too busy or if launching another virtual desktop session would weaken the performance of existing sessions.
You can prevent most of these connection problems with just a little pre-planning, and good remote desktop troubleshooting skills help when other issues come up. Make sure your SSL certificates are updated, configure firewalls correctly and keep an eye on your VDI capacity.
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