See this page at: http://ayesha.phys.virginia.edu/~bryan/vnc/

Remote Management With VNC

1. Wha?

VNC stands for Virtual Network Computing. It is, in essence, a remote display system which allows you to view a computing 'desktop' environment not only on the machine where it is running, but from anywhere on the Internet and from a wide variety of machine architectures.

• Chiefly useful for remote management. Allows you, for example, to manage a remote NT server from another computer (Windows, Mac or Unix) on the network.
• Clients and servers exist for many platforms:
  • Win95/98/NT
  • Mac
  • Un*x
  • Web interface (requires no special client software)
• Allows relocatable sessions:
  Can disconnect from a client session at one computer and resume at another.
• Client is small.
• Multiple clients can connect to the same server.
• Source code is available.
• It's free!

2. Installation

• Can be downloaded from VNC web page.
• Binaries are available for many supported platforms, plus contributed binaries for unsupported platforms.
• Installation kit includes viewer, server and other utilities for a given platform.
• Licensed under the terms of the GNU General Public License (GPL).
• Installation under Windows is simple: just unpack zip file and run setup. Under Un*x, just copy binaries into an appropriate directory on the search path. Instructions are included with the Installation kit.

3. Demos

• VNC viewer on local machine, viewing remote NT server.
• Web browser on local machine, viewing remote NT server.
• VNC viewer on local machine, viewing remote Linux computer.

In the remainder of this document, we'll be speaking exclusively about the Windows implementation of the VNC client and server, unless specified otherwise.

4. Server Settings

Connections:
• Accept socket connections: Should always be on. Only applicable to internal ATT version of the server, which optionally communicate via CORBA instead of sockets.
• Display Number / Auto: Changes port numbers on which VNC server listens. Defaults are port 5800 and 5900. These are analogous to display number 0 for X servers (on which VNC is based), which listen on port 6000. If you change the display number to 2, for example, VNC would start listening on ports 5802 and 5902, just as an X server running on display number 2 would listen on port 6002.
• Password: Connections to the VNC server are password-protected. The password is exchanged through a fairly secure challenge-response process, but subsequent traffic is unencrypted. VNC can, however, be used in conjuction with external encryption packages such as SSH. See the VNC web page for details.
• Disable remote keyboard and pointer: Allows "view only" sessions. Possibly useful in classroom situations, or for publicly-available status displays.

Updates:
• Default settings are usually best. Experiment only if you have problems.
• Note that you can request an update by clicking on a window's banner.
• "Poll on Event Received" is potentially useful for dialup connections.

Server can be installed as a service:
• Click on "Install WinVNC Service" from the Start Menu.
• You'll need to reboot or start the service from the services control panel to activate the WinVNC server.
• Advantages of running as a service:
  • You can actually log in or out of the remote NT session.
  • Can lock/unlock the screen of the remote server.
  • Each user can have his/her own VNC preferences. (This requires the installation of a VNC helper application.)
• Caveats:
  • If a user's login changes the screen resolution, all viewers are disconnected, and the user has to reconnect after login.
  • If user preferences specify a non-default display number, all other VNC users will be disconnected when that user logs in.
  • When VNC server is running as a service, you can't also start it up as an application.

Advanced Server Options:
• AuthRequired: Can allow passwordless connections.
• AllowLoopback: Can allow vncviewer to look at local VNC server.
• AllowProperties: Can be set to prevent user from changing server properties.
• AllowShutdown: Can be set to prevent user from shutting down VNC server.
• AuthHosts: Used to limit access to the VNC server, based on IP address.
• LockSetting: 0=none, 1=lock on disconnect, 2=logoff on disconnect.
• and many others...

5. Viewer Settings

Connection Options:
• Request shared session: By default, when one user connects, others are disconnected. Shared sessions allow multiple users to see the same display.
• 8bit: Forces color depth to be 8 bits. This can improve performance on slow network connections.
• Scale by: Allows remote console display to appear smaller on the local display. Not really very useful, since it tends to make the remote display illegible.
• Full Screen: See the resulting pop-up box for instructions about exiting from this mode.

6. Warnings

• Be mindful of security. Although VNC encrypts the password you use to connect to the VNC server, subsequent traffic is not encrypted. See the VNC web page for some information about using VNC with SSH. For a free SSH daemon for WinNT, see the cygwin tools and the instructions at this site:

  http://www.gnac.com/techinfo/ssh_on_nt/ssh_on_nt.htm
  

  We're just starting to experiment with this in our department.
• Although the VNC web pages say lots of glowing things about VNC as a tool for connecting to remote Unix machines, don't believe it. I'm sure it's good for the situation they're using it under at ATT, but it's not appropriate for the way most people work around here. Use Hummingbird Exceed instead. It has much more satisfactory performance, and it doesn't bog down the remote machine. See the following diagrams for a comparison of the ways VNC and X work.