When running the jenkins agent, I receive the following error:

p.ngsmedicare.com
java.io.IOException: http://kyettsjenlx01v.corp.ngsmedicare.com:9080/ provided port:33828 is not reachable on host kyettsjenlx01v.corp.ngsmedicare.com
        at org.jenkinsci.remoting.engine.JnlpAgentEndpointResolver.resolve(JnlpAgentEndpointResolver.java:311)
        at hudson.remoting.Engine.innerRun(Engine.java:751)
        at hudson.remoting.Engine.run(Engine.java:543)

If we open that port in our firewall/jenkins server, the error appears with another port number.

It seems like ports are being randomly generated which doesn't work in a stateful firewall. 

How do we resolve this? Is there a range of ports that should be opened?