

Given that sort of description I’d bet that it is DNS actually. If you run a DNS lookup from your LAN for your domain, do you get the external IP or the internal one? You can try this with dig in Linux or nslookup in Windows (I think).
If I’m right and you’re getting the external IP even when querying from your LAN, then what you need is either a separate DNS for your LAN or what they call a “split DNS” whe are a your domain server returns a different value depending on the originating IP.
You can check for this by editing your hosts file. If you add your domain and local IP there and then try to ping that domain on that machine, it should work. If you’ve got a small network, you might even just copy the hosts lines between machines (this is what I do for example).











I hadn’t noticed, but now I can’t unsee it.