The server instances are using UDP broadcasts in order to inform other nodes about urgent events, such as start and stop, as well as system failure or crash immediately.
The default port for communication is port 5124. You can change this in the INI file or on the command line.
All communication between the nodes is done over TCP/IP on the same port.
Verify that you have no firewall blocking this port
or change the port on all server installations to a different number
better matching your environment.
