ipv6 nat (nat66) by FreeBSD pf

although nat66 is still under draft, but FreeBSD pf already support it for long time.
(edit the pf.conf and insert following codes)

v6_wan_if="your-v6-wan-interface-name"
v6_wan_ip="your-v6-wan-ip-address"

no nat on $v6_wan_if inet6 from $v6_wan_ip to any
nat on $v6_wan_if inet6 from any to any -> $v6_wan_ip    

You are all set!