Some hosting providers, like Online in France provide IPv6 access via prefix delegation. You get a DUID that has to be sent to their DHCP server. The IP address is configured by the client.

The recommended method is using Dibbler, but this solution is pretty buggy.

On Ubuntu or Debian, you can use the provided dhclient to obtain the prefix delegation.

Below are samples of dhclient6.conf and interfaces. Note that in this configuration everything is configured by the client, but you could request a name server from the DHCP server.

/etc/dhcp/dhclient6.conf:

interface "em1" {
    send dhcp6.client-id your:duid;
    request;
}

/etc/network/interfaces:

auto em1
iface em1 inet6 static
    address your:ip:v6:address
    netmask your_nemask
    accept_ra 1
    pre-up /sbin/dhclient -cf /etc/dhcp/dhclient6.conf -6 -P em1