Exposing dynamic ports at run-time

I have an application that will create a listener based on user action. It will create this listener on a random port. There can be several listeners established depending upon the scenario. Will these listener ports be available from the network even though they were not defined when the container was started? Basically, I want to communicate to an agent on another physical machine the port it needs to connect to back on my machine. I can find all kinds of documentation about defining the ports during startup, but I have not been able to find anything about how dynamic ports created during runtime are handled.