ZyXEL Communications P-334WT Support Notes page 102

3. View dynamic ports opened by UPnP
When using UPnP, if the ZyXEL device is configured as "Allow users to make configuration changes through UPnP", the device will accept any port opening request
sent by UPnP protocol. And actually, such behaviour also add some risks to your internal LAN. For security sake, we provide a CI command for users to view currently
opened ports.
Please go to SMT menu, and type this command, "ip nat server disp" to display the dynamic port mappings. Please note that, the UPnP dynamic port mappings start from
item 13 to 35.