Why does Media Server report “binding failed”?

If the Media Server needs to allocate a port for media transmission, and cannot bind, it will generate a log message such as:

This is due to some other application already binding to some ports in the 7000-7499 range. Typically it is the Microsoft DNS server doing this.

To check which ports are bound at any point in time, you can run the following command from the DOS prompt:

Microsoft Windows allows you to define which port ranges will NOT be returned to any application/service that requests a random port number, via the following registry entry:

To ensure correct functionality, you should add the following ranges, without removing whatever the value already contains:

5060-5060 (or the SIP Port for 3CX PhoneSystem)
3478-3478 (STUN / Firewall Checker)
7000-7499 (or the range of RTP ports for Local Connections)
9000-9015 (or the range of RTP ports for External Connections)

…so if the value already contained “1433-1434”, the end result would look something like this:

For more specific instructions regarding this registry entry, refer to:

http://support.microsoft.com/kb/812873/

General 3CX Phone System FAQs