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Control Web and Windows XP Service Pack 2
 There are some important and useful security enhancements included in the Windows XP Service Pack 2. Probably the most important enhancement is the newly included Windows Firewall. The firewall is a software layer, which limits the information transfer between your computer and the rest of the network or the whole Internet. It also prohibits users from outside world to access your computer. The aim of this article is to demonstrate the basic principles of firewall configuration to successfully run the Control Web process control system on the computer with Windows XP SP2.

There are situations, which require the remote access to the computer. For example, if the WWW server is a part o the Control Web application, it is necessary to allow users to access it from their computers. Another example is deploying of distributed applications — one application is divided into several parts, each running on the separate computer. Individual applications need to share data, to notify about events etc. It is necessary to configure the firewall to allow communication over network.

Thorough description of firewall principles and configuration can be found in the documentation published by Microsoft Corporation.

WWW server — the HTTPD virtual instrument

The httpd virtual instrument, working as WWW server, is a part of both Control Web 5 and Control Web 2000 distribution. If you include this virtual instrument into your application and run the application under Windows XP SP2, Windows Firewall blocks the access to the web server from other computers. It also opens the following warning dialog box:

If the user with administrative privileges is logged to the system (either the Administrator or an user, who is a member of Administrators group) he or she can directly unblock the Control Web application. The Firewall adds the Control Web to the list of applications with allowed access to the network services. All other runs of the application will perform without any problems with network access granted.

Remark:

Control Web disappears from the Firewall application list when it is un-installed. If you un-install the application and install it again, it is necessary to unblock it again.

If the currently logged user does not heave administrative privileges, Windows Firewall displays notification message box. Only administrators can allow applications to access network. It is necessary to log on as Administrator to unblock Control Web.

To unblock an application manually, open Windows Firewall applet from Control Panel (Control Panel can be opened from menu Start -> Settings -> Control Panel).

Remark:

Windows Firewall applet is not directly accessible if the Control Panel is in the Category View mode. Switch it to the Classic View mode or open the Windows Security Center first an then open Windows Firewall applet:

Application allowed to access the network are listed in the Exceptions tab. It is necessary to add Control Web to the list of unblocked applications.

Please note it is necessary to unblock both development and runtime versions of Control Web separately. The development version main executable (cw5.exe) and runtime version main executable (cw5run.exe) are completely different applications from the Firewall point of view.

Distributed applications

Configuration is more complex in the case of distributed applications. Individual applications use the Control Web IPC Service to establish the communication so it is necessary to unblock it.

Control Web IPC Service

The Control Web IPC Service is a part of every Control Web installation. It runs even before any user logs into the system as an operating system service. Control Web IPC is quite small program, but is used by both development version and runtime version of Control Web to communicate with operating system, to establish mutual network connections etc.

The Control Web IPC Service process is implemented in the cwsvc.exe file. It is installed in the directory \Program Files\Moravian Instruments\shared.

It is necessary to unblock this service (add it to the list of applications allowed to access network) in the Windows Firewall configuration. Steps necessary to unblock some application are described in the previous chapter.

 
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