pfSense

When using Track Interface as a IPv6 Configuration Type in the LAN interface, the DHCPv6 server doesn't merge the IA_PD-prefix obtained via the DHCP6 client (WAN interface) and the DNS Servers input (i.e. ::a and ::b) in the DHCPv6 configuration page.

If user fills ::a and ::b as DNS servers in the DNS Servers field, the configuration file will be written without the prefix obtained via Track Interface
(::a and ::b instead of expected results 2001:14ab:11f1:9200::a and 2001:14ab:11f1:9200::b in case 2001:14ab:11f1:9200::/56 being delegated and Track Interface with WAN/0 used as IPv6 configuration parameters for the LAN interface).

The merge works ok with the DHCPv6 Range and static mappings fields and provides ability to assign semi static IPv6 addresses for the internal DNS servers, but it doesn't work in the DNS Servers field and as such manual reconfiguration is required each time the ISP delegates a new IPv6 network.

/var/dhcpd/etc/dhcpdv6.conf:

subnet6 2001:14ab:11f1:9200::/64 {
range6 2001:14ab:11f1:9200::fe90:0 2001:14ab:11f1:9200::fe90:ffff;
do-forward-updates false;
option dhcp6.name-servers ::a,::b;

}
host s_lan_0 {
host-identifier option dhcp6.client-id 00:01:00:01:1b:de:af:2b:20:c9:d0:54:c6:d3;
fixed-address6 2001:14ab:11f1:9200::a;
option host-name DNS1;
}

This is problematic when the ISP doesn't obey the request for delegating previously assigned network for the customer and causes the DNS name resolution to fail after the new IPv6 network will be delegated for the customer.