Modbus passive (scanning) mode - do you use it?

A colleague of mine asked me to support a passive (scanning) mode for Modbus (RTU/ASCII) in our D2000 communication driver. So I did this week. This way he can use e.g. Moxa NPort to eavesdrop on existing serial communication. The driver analyzes both Modbus requests (starting address & number of registers are obtained) and responses (with data).
In the future, should the existing communication be discontinued, we can simply reconfigure & rewire the Moxa, disable the "Passive mode" option and start active communication.

Do your SCADA systems also support this feature? Or do you use 3rd party devices, like some Modbus multiplexers/proxies if such a thing is needed?
Many of our (ICC) gateways support a Modbus RTU Sniffer driver that allows passively listening in on the Modbus communication between a master and one or more slaves in order to "sniff" the data exchanged. This driver is frequently used for multi-master applications where one or both of the masters is monitor only and for applications where a customer needs to monitor slaves in an existing Modbus network without impacting the communications. And because it's a gateway, the second master doesn't necessarily have to use Modbus, it can use any other protocol such as BACnet, PROFINET, EtherNet/IP, etc.

The ICC Mirius and ETH-1000 are a couple examples of gateways that supports the Modbus RTU Sniffer driver: