Ethernet
subnetMask() - Ethernet
Ethernet.subnetMask() returns the subnet mask of the network as an IPAddress.
SerialLogHandler logHandler;
void setup() {
// Wait for a USB serial connection for up to 30 seconds
waitFor(Serial.isConnected, 30000);
// Prints out the subnet mask over Serial.
Log.info(Ethernet.subnetMask());
}