If you add or configure a serial port that is backed by a remote network connection, ESXi firewall settings can prevent transmissions.
Before you connect network-backed virtual serial ports, you must add one of the following firewall rule sets to prevent the firewall from blocking communication:
- VM serial port connected to vSPC. Use to connect the serial port output through a network with the Use virtual serial port concentrator option enabled to allow only outgoing communication from the host.
- VM serial port connected over network. Use to connect the serial port output through a network without the virtual serial port concentrator.
For details about allowing access to an ESXi service through the firewall, see the vSphere Security documentation.