Enabling the DMXDisplayCluster plugin is typically enough. When the plugin is enabled, by default it does the following:
- It receives DMX on the primary only
- It forwards DMX to any secondary via cluster events within the same frame, keeping everything sync
- It blocks any secondary from receiving possibly conflicting DMX from the network
When using the DMX Fixtures examples from engine content, you will likely want to overscan in nDisplay to have the lights show on all nodes.
The command line args you found are there to specify a different primary node for DMX. This allows you to have a separate nDisplay node that is responsible to handle DMX. If you set a separate -dc_dmx_primary you will also want to define any other node as -dc_dmx_secondary.