New OpenWRT user here. I recently setup OpenWRT stable 19.07.3 on a cheap TP-Link Wireless Access point to act as a NAT gateway for my home network. Everything has been working well, except one outgoing RDP (Windows Remote Desktop Protocol) connection that I usually make to a host outside my network on an unconventional port (15112).
I have no special setup besides a LAN and WAN zone, and Network Address Translation from LAN -> WAN.
To troubleshoot, I tried the following:
- Making RDP connections to external hosts on the standard RDP TCP port (3389) works fine from behind my openwrt NAT gateway
- Making a TCP network connection on port 15112 to a linux box on the internet works fine from behind my openwrt NAT gateway.
- Making RDP connections to the external host on the port 15112 works with two other NAT routers I've tried that are running proprietary (and I assume permissive) software.
Clearly OpenWRT knows how to NAT traverse RDP since it works to connect with hosts who use the conventional 3389 port. So what do I need to make it work on an arbitrary port?