Control.com - Nerds in Control

How do I tell when two ControlLogix's communicating via DH+ loose communication?

I have found that someone posted the following answer in a previous old post:

The methods I use in SLC5, PLC5 and ControlLogix is first monitor the Active Node status bit, which is a status bit in SLC5s and PLC5s, and by using a CIP attribute MSG to the DHRIO module with ControlLogix. Next set up a "heartbeat" bit in the MSG between PLCs, have the bit toggle at a rate that suits your message rate, and monitor this with a timer.

My question is:

What are the class/instance/attribute codes to configure in the ControlLogix message to monitor the active DH+ nodes using the 1756-DHRIO? Also is this a CIP generic message? Is this CIP message pointed directly to the 1756-DHRIO module?