Since RHEL has default personal agent installed on port 5555, it defaults to 5556 , this leads to situation where build forge would require to control agent on different ports (Windows on 5555 ). You have option of defaulting to 5555 after agent is installed which is mentioned here .
However if you still want to have it work on 5556 , there isn't direct configuration that lets you set port for each agent that you want to control , instead there is simple way to specify in the server console . One can navigate to "Servers" and click on "Add Server" , while you specify host in the details tab, mention fully qualified server host name along with port number in the format <fully qualified server name>:<host port> . Also with this you should even be able to control multiple agent on same server having different version of agent installed.