IPv6 - multi prefix delegation options

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[X] I have read the contributing guide lines at https://github.com/opnsense/core/blob/master/CONTRIBUTING.md
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Is your feature request related to a problem? Please describe.

For the purposes of IPv6 and pulling Ipv6 prefixes from my ISP (AT&T), I need a solution in which OPNSense makes the PD requests so that the Residential Gateway (AT&T RG "black box" device) will actually "activate" my available prefixes. No matter what settings I make on the DHCPv6 client config for the WAN (under basic), the RG will at most only activate a single IPv6 prefix.

Currently, I have to use a custom DHCPv6 client config override file that makes those PD requests so the prefixes get "activated" on the RG device. I only request 8 prefixes, because even though AT&T will give you a /60, it reserves 8 of them for itself. Customers only get to use 8 of the 16 prefixes.

interface ixl0 {
    send ia-na 0;
    send ia-pd 0;
    send ia-pd 1;
    send ia-pd 2;
    send ia-pd 3;
    send ia-pd 4;
    send ia-pd 5;
    send ia-pd 6;
    send ia-pd 7;
    #request domain-name-servers;
    #request domain-name;
    script "/var/etc/dhcp6c_wan_script.sh";
};
id-assoc na 0 { };
id-assoc pd 0 {
    prefix-interface ixl3 {
        sla-id 0;
        sla-len 0;
    };
};
id-assoc pd 1 {
    prefix-interface ixl3 {
        sla-id 0;
        sla-len 0;
    };
};
id-assoc pd 2 {
    prefix-interface ixl3 {
        sla-id 0;
        sla-len 0;
    };
};
.
.
.
id-assoc pd 7 {
    prefix-interface ixl3 {
        sla-id 0;
        sla-len 0;
    };
};

Describe the solution you like

It would be nice if there was something like the above already built in, and I could simply tick the boxes/make drop-down selections on what interfaces to make the PD selections to, and how many. In my case, they all go to the same interface, since I'm not using OPNSense to manage VLANs. I just need the prefixes made available on the RG. If you were using OPNSense to manage all of your VLANs, then each "id-assoc pd #' line would relate to that specific VLAN interface.

Describe alternatives you considered

Using this custom dhcpv6 client config override file is the only thing I've found that works.

opnsense / core

IPv6 - multi prefix delegation options #7647