In reForis, you can add IP addresses how many you want for a custom forwarder in the DNS tab. Unfortunately, there are two soft limits. 1. Knot Resolver is able to forward to 4 IP addresses at once. No matter if it is: a) 4x IPv4 addresses, 0 IPv6 addresses b) 2x IPv4 addresses, 2 IPv6 addresses and so on. There is a possibility to use semi-experimental case, which is explained at: https://knot-resolver.readthedocs.io/en/stable/modules-policy.html#forwarding-to-multiple-targets which means that traffic is randomly split to different providers and each group is limited to four IP addresses. 2) Resolver-conf used in Turris OS counts with 2 IPv4 addresses and 2 IPv6 addresses. For now, let's limit it to have max 2 IPv4 addresses and 2 IPv6 addresses.