``--vdev`` parameter to the EAL when starting the application. The device name
must start with the *net_failsafe* prefix, followed by numbers or letters. This
name must be unique for each device. Each fail-safe instance must have at least one
-sub-device, up to ``RTE_MAX_ETHPORTS-1``.
+sub-device, and at most two.
A sub-device can be any DPDK device, including possibly another fail-safe device.