Simulating network packets in a packet processing pipeline

Simulated network packets may be processed via a network processing pipeline. A packet processor may implement packet processing stages to process network packets received via physical network interface at the packet processor. A controller for the packet processor may provide simulated network packets to the packet processor for processing at the different packet processing stages, bypassing the physical network interface. Dummy simulated packets may be provided to or generated at the packet processor on behalf of the controller to be parsed, processed, and returned to the controller. Metadata simulated packets may be injected into the packet processing stages and recaptured in storage locations that are accessible to the controller.