Not all Modbus Ethernet Bridges behave the same when a request to a device that is not available through the bridge is made. 

A bridge may:

Respond and report that the device is not present.

Not respond at all.

The following global parameter is available to define bridge response for a TCP/IP address.

MBETH_NORESP_xxx.xxx.xxx.xxx (where xxx.xxx.xxx.xxx is the IP address)

For	A Modbus Ethernet bridge
Purpose	Should the device communication interface request data from a device communicating through a bridge at the given TCP/IP address and no response is received, the software will declare only the device queried as down. Without the global defined as shown, all devices connected to the bridge will be declared down.
Value	Y

Important: When this global parameter is enabled, if the bridge is off, it will take longer for the device communication software to detect that all devices communicating through the bridge are down. This is because the software cannot distinguish bridge down scenarios from single device down scenarios because of bridge functionality.

More information

	Unsolicited Communication.
	About Modbus TCP/IP Communications.

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