Avanti 4.0 restricts port access to the local host only.  This is accomplished by only binding to the 127.0.0.1 interface, rather than all available interfaces. It means that outside of the localhost, it appears that the port has not been opened at all.

The port can be open for network wide access by enabling the allow_remote property under each serial ports Advanced properties settings.  Allow network access to the ports is a security issue, particularly with the console port (OPA0/tty00).