in "/usr/X11R6/lib/X11/doc/RELNOTES". Note particularly that "tcp",
as in "X -nolisten tcp" or "xhost +tcp/host:0", now means *both*
IP transport protocols. Use "inet" or "inet6", instead, to specify
only one or the other.
XDMCP support for IPv6 -- such as it is -- is disabled, just as
it is in the native, out-of-the-box build. XDM-AUTHORIZATION-1
does not really support IPv6 addresses, in any case. (It is
possible to build "xdm" with -DIPv6, but that presumes support
for IPv6-mapped IPv4 addresses in the default installation, for
one thing, and there are unexplored issues with all that.)