Deleting an event operation: specifying an available range of listening ports

Question

I have a client-server application using .NET remote transfer.

The server sends an update event to the client through .NET events. (This was a big challenge for the job, but it was deployed for seven months with no problems.)

To be able to listen to events, the client must create a listening channel. My app.config file points to port "0", which means "any available port."

All is well, but now network client administrators are trying to tighten firewalls. They asked if we could use a fixed port. I replied that it would be possible, but then you cannot have several clients working on the same machine. You also could not have multiple users using the application from the same Citrix server. (Please correct me if I am wrong)

Now they ask if I can specify the range of ports that the client application can select.

Does anyone know a simple way to do this: have the client create a listening channel on the first available port within the range?