Why VNC Cannot Connect

VNC (Virtual Network Computing) is a remote desktop sharing software that allows you to control another computer from a distance. A VNC server is installed on the computer you want to control and a VNC viewer is installed on the computer you want to use to access the remote computer. When you connect to a VNC server, your desktop is displayed on the VNC viewer and you can use it as if you were sitting in front of the remote computer.

Why VNC Connection Fails and How to Fix It

However, sometimes you may encounter a situation where you cannot connect to a VNC server. This can be frustrating, especially if you need to access the remote computer to troubleshoot a problem or perform a task. There are several reasons why you can't connect to a VNC server. The good news is there are also some solutions you can try to fix the problem.

1. Firewall Blocking VNC Connection

One of the most common reasons for a VNC connection failure is that the firewall on the remote computer is blocking the connection. By default, VNC uses port 5900. To allow VNC connections through the firewall, you need to open port 5900. The steps to do this will vary depending on the firewall software you are using.

Solution: Open Port 5900

1. On the remote computer, open the Control Panel.
2. Click on "System and Security".
3. Click on "Windows Firewall".
4. Click on "Advanced settings".
5. In the left pane, click on "Inbound Rules".
6. In the right pane, click on "New Rule".
7. Select "Port" as the rule type.
8. In the "Specific local ports" field, enter "5900".
9. Click on "Next".
10. Select "Allow the connection" as the action.
11. Click on "Next".
12. Select "Any" as the profile.
13. Click on "Next".
14. Give the rule a name and description.
15. Click on "Finish".

2. Incorrect VNC Port Number

If you are using a non-standard port number for VNC, you need to make sure that the VNC viewer is configured to use the same port number. You can check the port number that the VNC server is listening on by looking at the VNC server configuration file.

Solution: Check the VNC Port Number

1. On the remote computer, open the VNC server configuration file.
2. Look for the line that starts with "# listening port =".
3. The port number is the number after the equals sign.
4. Make sure that the port number in the VNC viewer is the same as the port number in the VNC server configuration file.

3. Outdated VNC Software

If you are using an outdated version of VNC, you may not be able to connect to a VNC server running a newer version of VNC. VNC is constantly being updated with new features and security patches, so it is important to keep your VNC software up to date.

Solution: Update Your VNC Software

1. Download the latest version of VNC from the VNC website.
2. Uninstall the old version of VNC.
3. Install the new version of VNC.

4. Incompatible VNC Versions

If you are trying to connect to a VNC server running a different version of VNC than the VNC viewer, you may not be able to establish a connection. For example, if you are using a VNC viewer from RealVNC and you are trying to connect to a VNC server from TightVNC, you may not be able to connect.

Solution: Use a Compatible VNC Viewer

1. Make sure that the VNC viewer and the VNC server are running compatible versions of VNC.
2. If you are not sure which version of VNC the VNC server is running, you can ask the system administrator.

5. VNC Server Not Running

If the VNC server is not running, you will not be able to connect to it.

Solution: Start the VNC Server

1. On the remote computer, open the Services window.
2. Look for the "VNC Server" service.
3. If the service is not running, start it.

Conclusion

If you are having trouble connecting to a VNC server, it is important to troubleshoot the problem step-by-step. By following the steps in this article, you should be able to identify and fix the problem.

FAQ on VNC Connection Issues

1. What is the most common reason for a VNC connection failure?

   • The most common reason for a VNC connection failure is that the firewall on the remote computer is blocking the connection.

2. What port does VNC use by default?

   • VNC uses port 5900 by default.

3. How can I check the port number that the VNC server is listening on?

   • You can check the port number that the VNC server is listening on by looking at the VNC server configuration file.

4. What should I do if I am using an outdated version of VNC?

   • You should update your VNC software to the latest version.

5. What should I do if I am trying to connect to a VNC server running a different version of VNC than the VNC viewer?

   • You should make sure that the VNC viewer and the VNC server are running compatible versions of VNC.