if port is monitored, UDT will collect data what endpoints (MAC addresses) are connected to that port.
If at least one port is monitored on a node, UDT layer2 job is periodically executed and data are updated for all monitored ports on that node. If no port is monitored on a node, layer2 job is canceled for that node.
If no port is monitored on a node, UDT layer3 job (if node is layer3 capable) will still be executed and you'll get IP addresses.
Hope this answers your question.
Thanks Bedrich for clarifying