FreeBSD, NetBSD and Darwin/Mac OS X (as well as probably OpenBSD9 use the stf0 (six-to-for) interface to configure 6to4. Good instructions on how to configure a stf-interface can be found at the following two weblocations:

http://www.netbsd.org/Documentation/network/ipv6/#typical2
and
http://onlamp.com/pub/a/onlamp/2001/06/01/ipv6_tutorial.html

6to4 with NetBSD’s 6to4-script (Perl)

The easiest way to configure 6to4 on NetBSD (may also work on the other OSes) is to install the Perl script called "6to4", that comes with NetBSD itself. The script uses a configuration file called 6to4.conf in which all the needed configuration information is collected and properly commented. On can install the 6to4 script either manually or from NetBSD’s pkgsrc system where it is found in /usr/pkgsrc/net/6to4.