The 6to4 script can be used to setup IPv6 on your home machine and net-
work for exploring IPv6 without any registrations. 6to4 is a mechanism by
which your IPv6 address(es) are derived from an assigned IPv4 address,
and which involves automatic tunnelling to one or more remove 6to4 hubs,
which will then forward your v6 packets on the 6bone etc. Replies are
routed back to you over IPv4 via (possibly) other 6to4 capable remote
gateways. As such, IPv6-in-IPv4-encapsulated packets are accepted from
all v4-hosts.

WWW: ftp://ftp.netbsd.org/pub/NetBSD/packages/pkgsrc/net/6to4/files/6to4.html