OpenNMS with Minion servers - firewall ports configuration

Hi All,
I have installed an instance of OpenNMS and multiple Minion servers to monitor remote servers in different networks.
I know from documentation that the ports used from the minion server to connect the OpenNMS server are 8980 and 61616.
I would like to know the port or the port range used from the OpenNMS server to connect the Minion server in order to restrict firewall rules.
I tried to block traffic on the firewall but I saw that OpenNMS server opens connection to the Minion server on different ports (not always the same).
could you help me? Is there a configuration file where I can set a port range used? If so, which is the path and the file name?
thanks for the support
Matteo