I think @Mkrtich would be able to help with this question? 🙂
Hi - I haven't been able to establish the difference between the Sagemcom F@ST 3864 HP and the F@ST 3864 V3 AC hardware or user software interface, so my comment is in relation to the V3 AC which may be different from the HP version; it may be that HP stands for High Power? If anyone reading this knows the difference, it would be interesting to know.
I couldn't find a way to edit the Optus DNS IPV4 or IPV6 DNS addresses in the Settings Menu of the Sagemcom V3 AC Router. This may not be unusal for a Carrier Router. However, the workaround this is that you are able to edit your PC or device Network settings from within their respective Network Settings and eidt them there. This means altering all device settings manually rather than what you were hoping to achieve once at the Router. I am not familiar with Open DNS but it appears they claim to offer a basic faster internet experience and a more enhanced and secure internet connection service if you have an account with them. I don't know if they offer Dynamic DNS.
The DNS Page under Advanced Settings in the Sagemcom V3 AC is for Dynamic DNS Server activation when you have an established account with the three providers listed in the drop-down box. This service is provided by companies who offer you a substitute pseudo external address that is mapped to your carrier's actual dynamic external IP address which can change during the day. The company's PC client software monitors the change and adjusts their server record with the new target destination setting accordingly, allowing the external pseudo IP address to remain constant to Internet . This generally allows users to access their home network and security cameras when they are not at home, basically anywhere in the world using the fixed pseudo IP address to connect to their home network.
On the Sagemcom V3 AC, it only appears to support the three companies listed in the drop down box and can not be edited.
Hope this helps.