When a Sensor is deployed inline, it monitors traffic at wire speed and, depending on your policies, prevents attacks from occurring. However, if the Sensor fails, depending on your configuration, the Sensor becomes a bump in the wire which results either in no traffic passing through or in all traffic passing through without being monitored. The former configuration is called inline fail-closed and the latter configuration is called inline fail-open.
To deploy Sensors in a fail-open configuration, you might require additional hardware which comprises a compatible fail-open switch, appropriate cables, and depends on which port you want to configure – SFP, SFP+, QSFP+, or QSFP28 transceivers. The only exception to this rule is if you decide to use the in-built fail-open option available in some Sensor models.
To deploy Sensors in fail-closed configuration, you will not require any additional hardware. When enabled, Sensor ports requiring the use of SFP, SFP+, QSFP+, or QSFP28 transceivers are configured inline fail-closed by default .