# Network interfaces for using Layer 2 Engines in Passive Engine mode

You can configure Layer 2 Engines in Passive Engine mode. In Passive Engine mode, the engine captures network traffic for inspection but does not actively filter traffic.

The most common way to configure a Layer 2 Engine in Passive Engine mode is to define Capture Interfaces for listening to network traffic that does not flow through the Layer 2 Engine. If you configure only Capture Interfaces, the engine always functions in Passive Engine mode. You can also use a Layer 2 Engine that has Inline Interfaces in Passive Engine mode. To do this, you configure the engine to only log connections.