During normal in-line fail-open operation of the Sensor, Control port on the Sensor supplies power and a heartbeat packet to the fail-open switch. If the fail-open switch does not receive 6 heartbeat signals within its programmed interval of 300 milliseconds, the fail-open switch removes the Sensor from the data path, and moves into Bypass Mode, providing continuous data flow with little network interruption.

While the fail-open switch is in bypass mode, traffic passes directly through it, bypassing the Sensor.

When normal Sensor operation resumes, you may or may not need to manually re-enable the monitoring ports from the Manager interface, depending on the activity leading up to the Sensor's failure.

The following section describes how to return the Sensor to in-line mode.