Fail-Open kits minimize the potential risks of in-line Sensor failure on critical network links. You need to purchase these kits separately. Copper versions of the kit are available for the one-gigabit ports.
Monitoring ports of the Sensors can be fail-close; thus, if the Sensor is deployed in-line fail-close, a hardware failure results in network downtime except the built-in RJ-45 ports which come with built-in fail-open functionality.
While the Sensor is operating, the active fail-open kit is in-line and routes all traffic directly through the Sensor. When the Sensor fails, the fail-open switch automatically shifts to a bypass state; in-line traffic continues to flow through the network link but is no longer routed through the Sensor. After the Sensor resumes normal operation, the switch returns to the in-line state, enabling in-line monitoring.
The NS3x00 Sensors have built-in RJ-45 ports with fail-open and support active fail-open when connected to an active fail-open kit.
Caution
Sensor outage breaks the link connecting the devices on either side of the Sensor for a brief moment and requires renegotiation of the network link between the two peer devices connected to the Sensor. Depending on the network equipment, this disruption introduced by the renegotiation of the link layer between the two peer devices might range from a couple of seconds to more than a minute with certain vendors' devices.
Caution
A very brief link disruption might also occur when links between the Sensor and each of the peer devices are renegotiated to place the Sensor back in in-line mode. This outage, again, varies depending on the device, and can range from a few seconds to more than a minute. The performance of the switchover from in-line to bypass and vice versa varies depending on the vendor.
You can find the installation and troubleshooting instructions for the kit in the guide that accompanies the kit.