DHCPv6 with persistent DELEGATION (ia-pd) or IP (ia-na)

individual address (ia-na)

vi /etc/dhclient.conf

interface "xenbr0" {
    send dhcp6.client-id ;
    request;
}

beware all you get with an ia-na persistent IP is a /128. we are missing a route for a given prefix, and eventually a default route.

delegated prefix (ia-pd)

use a decent DHCP client to tell your ISP about your DUID

vi /etc/dhclient.conf

interface "xenbr0" {
    send dhcp6.client-id YOUR-DUID;
    #request;
}

you can force a request for delegated prefix with dhclient -P

we are eventually missing a default route.

shared

you can obtain dns settings from DHCPv6 however no gateway

therefore, we still need to get RAs (without the need of the actual SLAAC allocation)