DNS problems on fresh install

[joaoa]

This is my first time using OPNsense and I have been struggling for 4 days now to set it up. I have the OPNsense router's WAN port connected to my LAN (it is behind another router for now while I am testing, but the upstream router is on 192.168.21.x). On an absolutely fresh install, with all the default settings, I seem to be unable to use the DNS resolver. I am testing using nslookup google.com 192.168.1.1 on an Ubuntu machine. If I set query forwarding in Unbound DNS I get a reply from nslookup. However, if I disable query forwarding, I get a reply from nslookup google.com 8.8.8.8 but nslookup google.com 192.168.1.1 says "server can't find google.com: SERVFAIL". I have tried this on different clients, all with the same result. Pinging both 8.8.8.8 and google.com (or any other page) from OPNsense works.

I have tried changing around some settings such as DNS servers, checking and unchecking the "Allow DNS server list to be overridden by DHCP/PPP on WAN" option, looking at the firewall liveview, which doesn't seem to be blocking anything on port 53. I did notice that sometimes, when I change settings (any settings) nslookup google.com 192.168.1.1 returns an answer for a while (about a couple of minutes) and then stops working again.

I am at a loss here. I have scoured the web and turned copilot inside out trying to find what is going on. Everywhere I am looking it seems a fresh install should work right out of the box, which is not the case. What should I do? Please help.