How to Troubleshoot a VNC Viewer

Resolve VNC viewer connection issues step-by-step.

The Virtual Network Computing software or VNC, provides a convenient and efficient way to access cross-platform PC desktops from a remote location. VNC is designed to deliver a user experience that is very close to working locally with the personal computer desktop. However, VNC may fail to connect, fail to update the VNC Viewer screen in real time, or display pixelated and discolored resolution under adverse network conditions. There are specific procedures you can use to troubleshoot, identify the root cause and resolve the issue.

Things You'll Need

• Microsoft Windows 7 VNC Viewer computer
• Microsoft Windows 7 VNC Server computer

Instructions

1. Click the "Globe" button on the Windows 7 VNC Server computer and then select "Search" and enter "cmd" in the "Search" box and then right-click on the command line icon that appears and select "Run as Administrator." The command line window appears.

2. Enter "netstat -bn" on the command prompt and tap the "Enter" key. Find the VNC service and its configured port number. If the VNC service is not listed, then enter "services.msc" on the command prompt and hit the "Enter" key. Scroll down to the VNC service in the window that appears and double-click on it. Select the "Start" button in the window that appears and then try again to establish a connection from the VNC Viewer. If the VNC Viewer is unable to connect proceed to the next step.

3. Enter "ipconfig" on the command prompt of the VNC Server computer, and tap the "Enter" key. Note the IP address displayed in the output. Then go to the VNC Viewer computer and enter "x.x.x.x::2222" in the "VNC Server:" field of the VNC Viewer substituting "x.x.x.x" with the VNC Server IP address and "2222" with the VNC service port number and tap the "Enter" key. If the VNC Viewer does not connect to the VNC Server, proceed to the next step.

4. Setup port forwarding on the firewall that protects the VNC Server from the Internet. The firewall should then forward requests received on the VNC Server port number to the IP address of the VNC Server. Note the Internet interface IP address of the firewall during firewall configuration.

5. Enter "x.x.x.x::2222" in the "VNC Server:" field of the VNC Viewer substituting "x.x.x.x" with the Internet facing IP address of the firewall and "2222" with the VNC service port number noted earlier, and tap the "Enter" key. If the VNC Viewer still does not connect to the VNC Server, proceed to the next step.

6. Select the "Globe" start button on the Windows 7 VNC Server, and then "Search" and then enter "firewall.cpl" in the "Search" box and then tap the "Enter" key. The Windows Firewall configuration window appears.

7. Select the "Exceptions" tab then select the VNC Server service from the list. If the VNC Server is not included in the list of programs, select the "Add Program" button, and then select the VNC Server service from the program list, and then select "OK." Select the VNC Server service box and select "OK".

8. Then go to the VNC Viewer computer and enter "x.x.x.x::2222" in the "VNC Server:" field of the VNC Viewer, substituting "x.x.x.x" with the IP address of the firewall and "2222" with the VNC service port number. Tap the "Enter" key. If the VNC Viewer does not connect to the VNC Server, proceed to the next step.

9. Select the "Globe" start button on the VNC Viewer computer, and then select "Search," and then enter "cmd" in the "Search" box and tap the "Enter" key. Enter "tracert x.x.x.x" at the command prompt, substituting the IP address of the VNC Server computer or firewall in place of "x.x.x.x," and tap the "Enter" key. The output displays an entry for every device IP address between the VNC Viewer and VNC Server. When output shows "* * * *" before displaying either the IP address of the VNC Server or the IP address of the firewall or router, that indicates that the network device represented by the "* * * *" may need to be reconfigured or replaced as it is not responding to network traffic. Once the device is reconfigured or replaced and tracert receives a reply from all devices along the network path, proceed to the next step.

10. Select the "Globe" button on the Windows 7 VNC Viewer computer, and then select "Programs," and then select the VNC program group icon. Click the "Run VNC Viewer" item, and the "VNC Viewer" application will display.

11. Select the "Options" button in the "VNC Viewer" window and the "VNC Viewer Options" window will appear. Select the "Color and Encoding" tab and then select the "Very low (8 colors)" radio button. Click the "OK" button to save the setting and then connect to the VNC Server computer from the VNC Viewer. If the performance is satisfactory, if there is no pixelation or slow screen refresh issues, then open the "VNC Viewer Options" window again and select the "Color and Encoding" tab and then select the "Low (64 colors) radio button. Then connect to the VNC Server computer from the VNC Viewer and test performance again. Repeat with the "Medium (256 colors)" setting, and the "Full (all available colors)" setting and save the setting that provides the best combination of performance and display resolution for the connection.

References

• RealVNC: VNC Server Free Edition 4.1 for Windows
• RealVNC: VNC Viewer Free Edition 4.1 for Windows
• Microsoft: Windows XP Professional Documentation - Tracert
• Microsoft: Windows XP Professional Documentation - Netstat