rp-docs: add info about hairpin-nat and local dns-record in debug sec…

…tion

Signed-off-by: Simon L. <[email protected]>

reverse-proxy.md

@@ -920,5 +920,6 @@ If something does not work, follow the steps below:
 1. If you use Cloudflare, you might need to skip the domain validation anyways since it is known that Cloudflare might block the validation attempts. In that case, see the last option below!
 1. If your reverse proxy is configured to use the host network (as recommended in the above docs) or running on the host, make sure that you've configured your firewall to open port 443 (and 80)!
 1. Check if you have a public IPv4- and public IPv6-address. If you only have a public IPv6-address (e.g. due to DS-Lite), make sure to enable IPv6 in Docker and your whole networking infrastructure (e.g. also by adding an AAAA DNS-entry to your domain)!
+1. [Enable Hairpin NAT in your router](https://github.com/nextcloud/all-in-one/discussions/5849) or [set up a local DNS server and add a custom dns-record](https://github.com/nextcloud/all-in-one#how-can-i-access-nextcloud-locally) that allows the server to reach itself locally
 1. Try to configure everything from scratch - if it still does not work by following https://github.com/nextcloud/all-in-one#how-to-properly-reset-the-instance.
 1. As last resort, you may disable the domain validation by adding `--env SKIP_DOMAIN_VALIDATION=true` to the docker run command. But only use this if you are completely sure that you've correctly configured everything!