@RMerlin,
Thanks for the info. Could you be little more helpful and instruct me how I can disable uPnP support on WAN1? I don't see that particular option anywhere.
Turn on Dual WAN? Then set uPnP off for Wan1?
I'm not sure why the concern. If Wan1 is not connected to the Internet, there should be no exposure.
ASUS does not expose the uPnP port to the Internet anyhow, so there is little risk there.
You can check uPnP exposure on this website: https://www.grc.com/default.htm