ssl:ip[:port]
    The specified SSL port (default: 6633) on the host at the given ip, which must be expressed as an IP address (not a DNS name). The --private-key, --certificate, and --ca-cert options are mandatory when this form is used.

tcp:ip[:port]
    The specified TCP port (default: 6633) on the host at the given ip, which must be expressed as an IP address (not a DNS name).

unix:file
    The Unix domain server socket named file.