To be honest, there’s no way to prevent others from using my DNS server without putting it behind a VPN or in any other non-public network. Also you can do port-knocking or something, but that's not rely authentication. However, I'm not aware of any authentication mechanisms in DNS. That would also cause performance to plummet. If you use a VPN or something, in turn, would mean you'd have to rely on someone else's DNS infrastructure. So I don't have any of this and its public.

The good thing about dnsdist is that it acts as a sort of load balancer for DNS queries and offers features such as dynamic blocking (including via eBpf) at the IP level and rules and rate limits for query types you can combine. Therefore, there are no limits (or very open limits) for all query types from whitelisted IPs, and stricter rules for all others. IPset and GeoIP banning of known malicious IPs and regions (using block-lists) also keeps the footprint of "unwanted" use very, very small.

They don’t, I guess