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Virtual Network Computing (VNC) is a graphical desktop sharing system that uses the Remote Frame Buffer protocol (RFB) to remotely control ...

Application Description

Virtual Network Computing (VNC) is a graphical desktop sharing system that uses the Remote Frame Buffer protocol (RFB) to remotely control ... VNC (Virtual Network Computing) is a technology for remote desktop sharing. VNC enables the desktop display of one computer to be remotely viewed.

System Requirements

System hardware meeting OS requirements
Windows compatible graphics card
Windows compatible network card
TCP/IP v4 network stack
Windows 98, Windows Me, Windows NT 4.0 Workstation / Server, Windows 2000 Professional / Server, Windows XP Professional / Home, Windows 2003 Server
Service Pack 3, 4, 5 or 6a is required on these platforms

Installation

VNC Server for Windows is installed as an optional component of the setup package. If VNC Server has been installed then a number of icons will be created for it under the Start Menu, at the location specified during installation (Usually RealVNC).

VNC Server for Windows is designed to run either in User Mode, as a personal per user server, or in Service Mode, as a system service available whether or not there is a user logged in.

The logged-on user can also choose to run their own personal User Mode server alongside an existing Service Mode server installed on the machine, provided that the two servers are configured to operate on different network port numbers.

Using VNC Server in User Mode

If you are just trying out VNC, or wish to provide access to your desktop infrequently for support or collaboration purposes, then you may find it best to run VNC Server in User Mode.

During the installation, leave the tickboxes which refer to the VNC Server System Service unticked, to prevent VNC Server being installed in Service Mode on your system.

When you want to use VNC Server, go to the VNC Server (User-Mode) program group (usually found under RealVNC in the Start Menu), and click on Run VNC Server. The VNC Server icon will appear in the system tray, to indicate that VNC Server is running.

At this point, you probably want to configure your personal VNC Server settings for User Mode. Right click on the tray icon and select Options, change the settings you want and click Apply or Ok. Note that you must at least configure the Authentication tab, otherwise you won't be able to connect in to your server this is deliberately the case, to avoid accidentally opening up your computer to attacks.

When you are finished with VNC Server, simply select Close VNC Server from the tray icon's menu.

Configuring VNC Server

VNC Server provides a number of options. These are usually configured via the Options... dialog, although they can also be specified directly on the command line of the WinVNC4 executable if required.

The Options... dialog consists of a number of pages of options, grouped according to their function. The following documentation describes each option and the equivalent command line parameters.

When the Ok or Apply buttons of the Options... dialog are pressed, any changed settings are saved to the registry. Unless otherwise specified, changed settings take effect immediately.

Connections

Accept connections on port
PortNumber=(port number)


Disconnect idle clients after
IdleTimeout=(seconds)

An idle client is one which has transmitted no keyboard or pointer events for more than a certain length of time. The VNC Server can be configured with a threshold, expressed in seconds, after which idle clients will be disconnected to conserve resources. If the threshold specified is zero seconds then connections will never timeout. The default idle timeout is one hour.

Serve Java viewer via HTTP on port
HTTPPortNumber=(port number)

If this option is ticked and the port number specified is non-zero then VNC Server will accept incoming HTTP requests, allowing the Java VNC Viewer to be downloaded by a Java-aware web browser. The Options... dialog will attempt to adjust the HTTP port to match changes made to the VNC port number.
Note that the HTTP port number cannot be set to the same value as that used for incoming VNC connections.
Only accept connections from the local machine
LocalHost=true|false

The LocalHost option tells VNC Server to only accept incoming connections from Viewers running on the local host computer. This is only normally used when connections are to tunnelled through a custom transport (e.g. serial line, custom wireless, etc) and will therefore appear to the TCP stack to originate from the local host. If VNC Server is configured to accept connections only via local loopback then the Hosts option is ignored.

Access Control
Hosts=(pattern)

VNC Server can filter incoming connection attempts based upon the apparent IP addresses of their originators. Which IP addresses are allowed to connect and which are not is determined by the Hosts pattern. The pattern consists of a comma-separated list of IP address specifications, prefixed by an action. Each specification starts with an action, gives an IP address, and a subnet-style mask. The first specification to match the address of the new connection determines the action that will performed.

Available actions are:


Reject the connection.
e.g. Hosts=+192.168.0.1/255.255.255.255,+192.168.1.0/255.255.255.0,-
The pattern given above allows the computer with address 192.168.0.1 to connect, as well as any computer in the 192.168.0.1 subnet. All other connections are rejected by the term, which is actually redundant in this case , a connection will always be rejected if it doesn't match anything in the Hosts pattern.
Note that IP addresses and masks are specified in
Type-A (xxx.yyyyyyyyy),
Type-B (xxx.yyy.zzzzzz) or
Type-C (xxx.yyy.zzz.www) form.
The specification 192.168 will therefore be interpreted as 192.0.0.168 rather than 192.168.0.0 as one might expect.
The Hosts pattern can be edited more easily through the Access Control interface, which allows IP address specifications to be edited individually and moved up (to match first) or down (to match last) the list.

Authentication

The Authentication page allows you to configure the required mode of authentication and level of security of VNC connections. VNC Open Server for Windows supports unauthenticated connections and classic VNC Password Authentication.

No Authentication
SecurityTypes=None

If your VNC Server is operating in a protected environment, such as a secure LAN or firewall protected network, then you may wish to configure VNC Server to accept connections without requiring a username or password to be specified.: We advise extreme caution when disabling authentication. Do not disable it unless you are absolutely sure that the host network is completely secure.

VNC Password Authentication
SecurityTypes=VncAuth

VNC Password Authentication allows a single password of up to 8 characters to be stored by VNC Server, which remote users must supply when prompted in order to authenticate.
The password to use can be configured by selecting Configure and typing the new password twice. On platforms which support it, the password (and all other configuration options) are protected using native operating system security methods, so that the password cannot be read or tampered with by other users.

NT Logon Authentication


Prompt local user to accept connections
QueryConnect=true|false

By default, VNC Server allows Viewers to connect as long as the correct username and password are supplied. QueryConnect allows an extra level of protection to be applied, requiring a local user to explicitly accept incoming connections.
When QueryConnect is enabled, incoming connections are first authenticated in the normal way. If the user authenticates successfully then a dialog is presented on the server's desktop, displaying the IP address and username of the incoming connection, and requiring a local user to accept the connection.
If the user does not accept the connection within a specified timeout then it is rejected. If an incoming connection requiring acceptance by the local user is received while an earlier connection is being queried then the second connection is automatically rejected, for security reasons.
Connections from specific hosts or subnets can be configured to be queried via the Hosts configuration setting.

Only prompt when there is a user logged on
QueryOnlyIfLoggedOn=true|false

This option affects the behaviour of the Query Connect option, if enabled. If this option is set then the local user will only be prompted to accept the incoming connection if they are logged in. If this option is not set then the local user will always be prompted, regardless of whether or not they are logged in.
Note that it is not possible to reliably detect whether or not a user is logged in on some older Windows platforms. On these platforms, this option will err on the side of security and always prompt the local user.
Query Connect Timeout=(seconds)
If Query Connect is enabled then the Query Connection dialog will be displayed by default for ten seconds before automatically rejecting the connection. The timeout value can be modified by setting QueryConnectTimeout accordingly.

Inputs

Accept pointer events from clients
AcceptPointerEvents=true/false

If this option is unticked then incoming pointer movements from all clients will be ignored, preventing any remote VNC Viewer from affecting the pointer of the VNC Server's desktop. This can be used to configure a server to become effectively view only.
Note that a client will still be deemed active for the purposes of the IdleTimeout setting if it is sending pointer events to the server, whether or not they are accepted.

Accept keyboard events from clients
AcceptKeyEvents=true/false

If this option is unticked then incoming keystrokes from all clients will be ignored, preventing any remote VNC Viewer from typing into the VNC Server's desktop. This can be used to configure a server to become effectively view-only.
Note that a client will still be deemed active for the purposes of the IdleTimeout setting if it is sending keyboard events to the server, whether or not they are accepted.

Accept clipboard updates from clients
AcceptCutText=true/false

If this option is unticked then incoming clipboard updates will be ignored from all clients. This option should be used when making a VNC Server effectively view-only, but may also prove useful to prevent clipboard changes made by clients from overriding the VNC Server's local clipboard when this would be undesirable or confusing.

Send clipboard updates to clients
SendCutText=true/false

This option, if unticked, prevents the VNC Server from informing clients of changes to its local clipboard contents. This can be useful when untrusted clients are to be allowed to connect to the VNC Server, since it prevents any private data being accidentally leaked via the clipboard.

Allow input events to affect the screen saver

This option determines whether keyboard and mouse events received from VNC Viewers can cause the screen-saver to be hidden. This option is actually a system-wide setting and is not implemented by VNC Server itself, so there is no equivalent command-line option. Some older Win32 platforms do not support this option. It is recommended that this check-box be ticked, so that the screen-saver can be disabled by VNC Viewer input.

Disable local inputs while server is in use
DisableLocalInputs=true/false

The mouse and keyboard physically attached to the server computer can be disabled for the duration of a remote connection, preventing local users from interacting with the computer.

Sharing

Always treat new connections as shared
AlwaysShared=true

If this option is set then all incoming connections will be treated as shared, and thus not disconnect any existing connections, regardless of whether the connecting VNC Viewer requested that the connection be shared.

Never treat new connections as shared
NeverShared=true

If this option is set then all incoming connections will be treated as non-shared. VNC Server will therefore either disconnect any existing connections, or refuse the incoming connection, depending on whether non-shared connections are configured to replace existing ones.

Use client's preferred sharing setting
AlwaysShared=false, NeverShared=false

When connecting, VNC Viewer specifies whether the connection should be shared or non-shared. If this setting is configured then the VNC Viewer's preference will be respected.

Non-shared connections replace existing ones
DisconnectClients=true/false

If an incoming connection is to be shared (either by choice or because AlwaysShared is set) then existing connections remain active. If a connection is non-shared (either by choice or because NeverShared is set) then either the new connection must be rejected, or existing clients disconnected.
If this setting is configured then existing clients will be disconnected when a new non-shared connection is made. Otherwise, they will remain, and the new connection will fail.

Desktop

While connected

Decorations such as wallpaper or font smoothing effects can make it harder for VNC Server to compress graphical data for trasmission to viewers. For viewers connected over slower networks, this can significantly degrade the apparent performance of the server. VNC Server can therefore simplify the desktop in several ways, to improve performance.

Remove wallpaper
RemoveWallpaper=true: This option causes VNC Server to remove any standard wallpaper bitmap that is set, as well as to disable Active Desktop components.
Remove background pattern RemovePattern=true: This option causes VNC Server to set the desktop background to a plain pattern while conenctions are active.
Disable user interface effects DisableEffects=true: This option causes VNC Server to disable desktop decorations such as font smoothing, window titlebar shading, menu animation, and so on.

When last client disconnects

These options are used to ensure that if VNC connections to a server are closed because of a network error, idle timeout, or even deliberately, then the computer will be left in as secure a state as possible. On Windows 2000 and above, it is possible for VNC Server to lock the workstation, leaving the current user logged in but requiring that their password be re-entered in order to access their programs or data. Alternatively, VNC Server can completely logoff the current user when there are no more VNC viewers connected, closing any running programs and leaving the workstation ready for another user to log in.

Do nothing
DisconnectAction=None

This option tells VNC Server not to perform any action.

Lock workstation
DisconnectAction=Lock

This option causes VNC Server to lock the workstation when the last VNC viewer disconnects.
Note that this option is not available on Windows 95/98/Me and Windows NT 4.

Logoff user
DisconnectAction=Logoff

This option causes the current user to be logged off when the last VNC viewer disconnects.

Capture Method

VNC Server is designed to support a variety of techniques for tracking changes to the local desktop. This release supports basic polling of the screen for changes, as well as the classic VNC Hooks technique.

Poll for changes to the desktop
UpdateMethod=0

If this option is selected then VNC Server will poll strips of the screen for changes. The polling mechanism attempts to minimize the load on the server computer while delivering a reasonable level of responsiveness.

Use VNC Hooks to track changes
UpdateMethod=1

This option tells VNC Server to use the classic VNC Hooks technique to track graphical updates. This scheme is more efficient than continuous polling but relies on certain properties of Windows applications and so can "miss" updates in some situations. VNC Hooks will also poll the screen infrequently to catch any missed updates.

Poll console windows for updates
PollConsoleWindows=true/false

The VNC Hooks hooking technique cannot track console windows because of limitations in the operating system. Instead, console windows may be polled for changes. If this option is set then VNC Server will track the visible parts of console windows and poll those areas for changes.

Use VNC Mirror driver to track changes
The VNC Mirror driver is not supported by VNC Open.

Capture alpha-blended windows
UseCaptureBlt=true/false

This option selects between two screen capture methods. If UseCaptureBlt is false then the faster of the two methods is used, which may in some cases cause alpha-blended windows and tool-tips not to be visible remotely. If UseCaptureBlt is true then these windows will be visible remotely but the VNC Server overhead will be increased.
Note that one aspect of the extra server overhead is that the local cursor will flicker if UserCaptureBlt is enabled.

Legacy

Import VNC Open 3.3 Setting

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