Local application (Prowlarr) can't connect after Opnsense router install

[Famousjaxx]

Would appreciate any wisdom with this.

Basically as per the title, I run the Prowlarr docker app on a raspberry pi device locally on my LAN. After replacing my $100 basic TP-Link router with OPNSense, Prowlarr is unable to connect to any of the 8 configured indexing sites. Example indexing sites are 1337x.to and apibay.org

The OPNSense router is basically a fresh install and as far as I know anything LAN interface side has full access to the internet. I've added a couple of port forwards from the WAN interface for VPN but nothing that should interfere with this.

The kicker is that if I put the TPLink router back in, everything works fine.

I'm getting the following errors through Prowlarr:

"Unable to connect to indexer, please check your DNS settings and ensure IPv6 is working or disabled. Resource temporarily unavailable (apibay.org:443)"

"Unable to connect to indexer, please check your DNS settings and ensure IPv6 is working or disabled. Resource temporarily unavailable (1337x.to:443)

Some points to consider
- DNS on my LAN points to the same raspberry PI device as it's running PiHole
- My WAN interface is configured with IPv4 DHCP and IPv6 none
- LAN interface is configured as IPv4 static 192.168.1.254/24 and IPv6 none
- IPv6 is disabled on the raspberry PI

If I remove the OPNSense router and replace back with the cheap $100 TPLink router Prowlarr is immediately able to connect to all indexers again which suggests to me that the config on the raspberry PI side and Prowlarr side is fine.

I did try adding temporarily a WAN interface firewall rule to pass all source all destination just to see if that would help incase something was being blocked but it made no difference.

Thanks in advance for any advice.

[Famousjaxx]

I fixed it by doing something so totally unrelated to OPNSense that I'm actually more confused than before.

In the docker compose file for PiHole, I had to map not only port 53 on the host to port 53 internally, but also the hosts IP address. In this case of course the host is my Raspberry Pi.

So the config line went from this:
"53:53/TCP"
"53:53/UDP"

To this:
"192.168.117.200:53:53/UDP"
"192.168.117.200:53:53/TCP"

I found this suggestion on an extremely obscure forum after working out that my containers DNS resolution wasn't working when the DNS server was set to the PiHole host IP but would work if I set it to something externally like 8.8.8.8.

The real head scratcher is why did this work without issue when the TP Link router was installed?

After hours of troubleshooting this is one question I'm happy to walk away from unanswered.

Thanks all!