Franck,
To the best of my knowledge, the FieldPoint ethernet modules should always respond to a ping. The cases I personally have seen in which there is no response to a ping is due to the processor being overloaded by the downloaded RT code ([c]FP-20xx series only), incorrect network settings (FP-160x and [c]FP-20xx modules), too much network traffic, corupted firmware, an offline network module and/or duplicated IP addresses.
Also, the ethernet network protocol used by FieldPoint does automatically include keep alive and status information. Depending upon the programming environment you are using, the status should be reported automatically. Thus the Pinging may be redundant.
Regards,
Aaron
LabVIEW Champion, CLA, CPI