This page provides information and discusses how you can have the NetCFax client use a fixed TCP port if required.

This is because the currently available and used versions of Windows cover the full range from the "stand alone versions" such as Windows 98/ME, Windows 2K Pro and even Windows XP Home, up to Windows XP Pro supporting Multi user capabilities via "Fast Task Switching" all the way up to the latest "server" systems such as Windows 2000 Server and Windows 2003 Server (including R2 and SP1/2)

However, because we understand that for security reasons it may sometimes be necessary to limit the number of TCP ports that are in use on any network, we are providing this insight into how TCP ports effect NetCFax.  

By default, every NetCFax client will have a TCP port in the range 1024 - 5000 assigned to it by the Windows Winsock when it is started up. It sends this information to the fax server it is logged into, and that server then uses this port to send all notification of fax activity etc to that specific client.

You may however change this and force the client to use a single specified TCP port for these notifications, but doing so is dependent on the computing environment you want the fax clients to work under, as detailed below.

If you use a NetCFax client and login to a fax server using a NetCFax login account that has administrator access rights, you can ONLY change this setting BEFORE YOU LOGIN to a fax server by going to the Tools menu - and selecting "Advanced Network Setup " option. The configuration window you will see is shown below :-

Just select the option you want "Use dynamic port..." or "Use specified...". If you choose Fixed, the lower TCP port field will automatically become accessible, and you need to enter the TCP port to be used in the field below.  

If you select dynamic, the two port fields below this option will become enabled, and you can change the range of ports that the NetCFax client can select a TCP port to be used from.  This allows you to limit it to a range of ports that are also open on a firewall or router.  (see the help page regarding firewalls for more detailed information on this important topic.)

When you save these settings, you may be warned that you MUST restart the NetCFax Client (not Windows itself) to have this changed setting used.  NB all other clients running on this machine and that may still be connected will NOT know about this change until they also restart their fax clients. 

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The environments the NetCFax client expects to find itself working in/under are as follows. 

1 - On a normal, (single user) style PC running Windows 98, Windows ME  or Windows 2000 Pro.  In this environment, only one Windows login account can be running the fax client, as logging off on these system closes all running programs automatically.

IN THIS CASE, IT IS JUST FINE TO HAVE THE CLIENT CONFIGURED TO USE A DYNAMIC PORT OR A FIXED TCP PORT FOR THESE SERVER NOTIFICATIONS.

2 - On an XP Pro system that DOES NOT HAVE Fast Task Switching (FTS) enabled, AND DOES NOT provide Remote Desktop Session (RDP) support.

As in case 1 above, only one Windows login account can be running the NetCFax client, as logging off on these system closes all running programs automatically.

IN THIS CASE, IT IS JUST FINE TO HAVE THE CLIENT CONFIGURED TO USE A DYNAMIC PORT OR A FIXED TCP PORT FOR THESE SERVER NOTIFICATIONS.

3 - On an XP Pro system that has Fast Task Switching (FTS) enabled, or even one that is able to provide Remote Desktop Session (RDP) support.

As opposed to the two previous cases above, This is a more complex environment that perhaps need some background providing so that you understand what happens. 

XP Pro uses what is called the "Terminal services support" system to provide the Fast Task Switching feature.  This means every Windows login account on that machine runs the same installed copy of any program, including of course the NetCFax client that is installed. Unfortunately, this environment does not provide what we would call true virtual machines, as all running FTS sessions have the same IP address, and there is only one set of TCP (and UDP) ports available for use.

Due to this, it is quite easy to understand the problem this can cause for the NetCFax client, as it is listening for the fax server notifications on what is known as a SOCKET, which is actually comprised of a combination of information that lets it be uniquely identified across the entire network.  The two most important of these are the the IP address and the TCP port.  It quickly becomes clear that if you have two separate instances of the same NetCFax client program running that have both the same IP address (which cannot be changed) and the same TCP port, they are not BOTH going to receive the notifications. This basic rule is in fact enforced by the Windows Winsock, which will not allow two programs to create or use a socket that uses the same IP address and port on the same machine.   Those same rules do however allow the same IP address PROVIDING the TCP port used is different.

IN THIS CASE, IF YOU HAVE THE CLIENT CONFIGURED TO USE A DYNAMICALLY ALLOCATED TCP PORT FOR THESE SERVER NOTIFICATIONS, YOU CAN RUN AS MANY INSTANCES OF THE CLIENT AS YOU WISH ON THIS MACHINE, including under different Fast Task switching accounts and remote RDP sessions, as each socket then does have a unique identity on the network.

IF HOWEVER YOU HAVE THE CLIENT CONFIGURED TO USE A FIXED TCP PORT FOR THESE SERVER NOTIFICATIONS, ONLY ONE INSTANCE OF THE CLIENT CAN BE RUN ON THIS MACHINE.

4 - On a Windows 2000 or 2003 Server (Most usually running as a Domain controller of some form) and supporting multiple RDP sessions.

As opposed to the cases above, This is probably the most complex environment that perhaps also needs some background providing so that you understand what happens. 

All of the comments and description shown above for XP Pro apply to Windows Server systems running Windows 2000 or 2003.

So again in this case, IF YOU HAVE THE CLIENT CONFIGURED TO USE A DYNAMICALLY ALLOCATED TCP PORT FOR THESE SERVER NOTIFICATIONS, YOU CAN RUN AS MANY INSTANCES OF THE CLIENT AS YOU WISH ON THIS MACHINE, including running it under multiple remote RDP sessions.

IF HOWEVER YOU HAVE THE CLIENT CONFIGURED TO USE A FIXED TCP PORT FOR THESE SERVER NOTIFICATIONS, ONLY ONE INSTANCE OF THE CLIENT CAN BE RUN ON THIS MACHINE, so only one RDP session will be able to run it.

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