UPC IPv6 prefix delegation and FreeBSD

Don’t believe the Connect-Box that you only get a /64 from UPC. Normal prefix delegation is possible, you just have to guess/experiment how big your prefix is. Here is my dhcp6c.conf

interface vr0 {
    send ia-pd 1;
    send ia-na 1;
#     send rapid-commit;
};

id-assoc na 1 {
};

id-assoc pd 1 {
 prefix ::/56 1800;

 prefix-interface vr1 {
   sla-len 4;
 };
};

My rtadvd.conf:

default:\
       :prefixlen#64:\

Some excerpts from my rc.conf:

ipv6_activate_all_interfaces="YES"
ipv6_cpe_wanif="vr0"
ipv6_gateway_enable="YES"
rtadvd_enable="YES"    
rtadvd_interfaces="vr1"