A passive fail-open switch depends on the Sensor to send a control signal or heartbeat signal from its Control port at regular intervals.
A passive copper or fiber fail-open switch receives a control signal every second. If the fail-open switch does not receive a signal for 4 seconds consecutively, it transitions to bypass mode thereby removing the Sensor from the path of traffic.
During normal operation, the bypass status of the switch remains ON. To confirm this, you must see the Control port LED ON on the switch. When the Sensor fails or reboots, bypass status is activated, which is indicated by the Control port LED going off. When the fail-open switch is in bypass mode, there is no traffic monitoring by the Sensor.
Note
Passive fail-open kits are not compatible with NS9600, NS9500, NS9x00, NS7600, NS3600, NS3500, and NS3x00 Sensors since these Sensors do not have control ports. Refer to the table which lists all fail-open switches and the Sensors with which they are compatible for more details.