To setup 6to4 under BSD with a properly configured kernel, simply do:

0) set ipv6=`printf "%x%x:%x%x" 192 144 140 19`
1) ifconfig stf0 create inet6 2002:${ipv6}:1::1 prefixlen 16
2) ifconfig ex0 inet6 2002:${ipv6}:2::1 prefixlen 64
3) route add -inet6 default 2002:c058:6301::	# 6to4 global anycast (near gw)