+dit(bf(-4, --ipv4) or bf(-6, --ipv6)) Tells rsync to prefer IPv4/IPv6
+when creating sockets. This only affects sockets that rsync has direct
+control over, such as the outgoing socket when directly contacting an
+rsync daemon, or the incoming sockets that an rsync daemon uses to
+listen for connections. One of these options may be required in older
+versions of Linux to work around an IPv6 bug in the kernel (if you see
+an "address already in use" error when nothing else is using the port,
+try specifying --ipv6 or --ipv4 when starting the daemon).
+