.IP "\fBssl:\fIip\fR[\fB:\fIport\fR]"
.IQ "\fBtcp:\fIip\fR[\fB:\fIport\fR]"
The specified \fIport\fR on the host at the given \fIip\fR, which must
be expressed as an IP address (not a DNS name) in IPv4 or IPv6 address
format.  Wrap IPv6 addresses in square brackets,
e.g. \fBtcp:[::1]:6633\fR.  For \fBssl\fR, the \fB\-\-private\-key\fR,
\fB\-\-certificate\fR, and \fB\-\-ca\-cert\fR options are mandatory.
.IP
If \fIport\fR is not specified, it currently defaults to 6633.  In the
future, the default will change to 6653, which is the IANA-defined
value.
.TP
\fBunix:\fIfile\fR
On POSIX, a Unix domain server socket named \fIfile\fR.
.IP
On Windows, a localhost TCP port written in \fIfile\fR.