A few days ago, I wrote an article about IPv6 NDP Proxy for a blog that I love to read. The problem discussed is that some routers who provide you an IPv6 prefix want to see the IPv6 addresses on the same L2 segment, so you can't use routing directly.
This problem can be encountered at OVH - an European dedicated server provider - if you want to set up virtual machines with IPv6 routing; or, if you have a Freebox - the set-top box provided by Free.fr provider - and want to use your own router behind.
In the article, I explain a solution based on the use of the NDP Proxy included in the linux kernel, with the example of a dedicated server at OVH.
Read the article (French)