During my last ITO project I worked on a solution to implement some kind of NAT
for IPv6. Packet-mangling solutions such as netfilter are missing IPv6 NAT for a good
reason: One of IPv6' design goals was the end-to-end principle and NAT often puts
people in the wrong feeling of security. NAT is one major reason why VoIP-breakhrough
came so late.
However, transparent proxying and redirection of connections is also done via NAT,
and thats where NAT for IPv6 makes sense: to setup SPAM-traps, transparent
virii-scanning or HTTP proxies. My solution works on Linux kernels >= 2.6.14,
running as a normal user-space daemon.