By default, RDM discovery is not enabled on the gateway. The previous models of Net3 DMX Gateways did have RDM discovery enabled by default.
How to enable RDM Discovery
Via Gateway's User Interface
Using the buttons on the gateway select the About menu option from the Home screen. Then select RDM Info.
The screen should appear similar to the image below. Ensure that both RDM and Background are enabled/on.
Via Net3 Concert
Select the gateway's icon in the World View map. Using the Property Editor, expand the port you wish to configure for RDM discovery. Now expand the line that says "Port # RDM Settings."
The screen should appear similar to the image below. Ensure that both RDM Enable and RDM Background Enable have been checked. If RDM Background Enable is not selected, then the Gateway will only poll for new RDM devices on that port when the Gateway starts up - so if a new device is added to the chain later, the Gateway will not know about it.