The Debian package of x2vnc is patched to support IPv6. At this point
there are no -4 or -6 options, or similar, to force the use of a
particular protocol. Literal IPv6 addresses can be specified using
brackets, e.g. [2001:cafe:beef::1]:0 for display 0.

 -- Magnus Holmgren <holmgren@debian.org>, Sat, 29 Oct 2016 17:12:31 +0200