Interface-based policy only defines what and how IPS functions are applied to the packets transmitted by the interface. It works no matter if the port is used in a forwarding path or used as an One-Arm device.

To enable One-Arm IDS, the user should first enable sniff-mode on the interface,

Once sniff-mode is turned on, both incoming and outgoing packets will be dropped after IPS inspections. The port can be connected to a hub or a switch's SPAN port. Any packet picked up by the interface will still follow the interface policy so different IPS and DoS anomaly checks can be applied.