OK, I don’t understand what excluding local addresses has to do with security. It’s not that unusual to route within the network.

https://github.com/LemmyNet/activitypub-federation-rust/blob/0.5.10/src/config.rs#L207

I’ve tried a few things now, hardcoded proxy headers:

  proxy_set_header X-Real-IP $custom_real_ip;
  proxy_set_header X-Forwarded-For $custom_forwarded_for;

setting the IP for the domain in the container:

    extra_hosts:
      - "rollenspiel.forum:142.132.206.141"

setting the DNS server in the container:

    dns:
      - 8.8.8.8

it doesn’t change the error message, I don’t know what Lemmy checks to determine that it’s a local IP, because all standard tools show me the public IP for rollenspiel.forum.