P4 Actions

This section describes the P4 actions in the Hello World Reference Pipeline using an example NACL table and rules set in it. Each row in the table represents a packet flow and each packet flow is described using a packet flow diagram.

Table 1. NACL Table With Example Rules
Index	DMAC	SIP	DIP	SPORT	DPORT	Action
0	00:00:00:00:10:02	1.2.3.4	2.3.4.5	345	456	Redirect
1	00:00:00:00:10:04	5.5.5.5	1.2.1.2	486	524	Permit
2	00:50:00:00:10:23	3.5.6.2	4.2.0.8	989	835	Drop
*	*	*	*	*	*	Drop ¹
* indicates that this example pipeline drops all packets that do not match any rule.

The Pipeline highlights some of the basic capabilities of P4 and implements the following actions when a packet matches all the attributes:

Redirect – Rule Match
- Packet is sent to Arm® Data Path Application (DPA) Software for further processing.
  Note: This reference pipeline does not have accompanying DPA code and so packets sent to the Arm CPU complex for processing using the pipeline Redirect action are dropped.
Permit – Rule Match
- If a packet is received on the DPU port Eth 1/1, it is sent out on port Eth 1/2.
- If a packet is received on the DPU port Eth 1/2, it is sent out on port Eth 1/1.
Drop – Rule Match
- Packet is dropped.
Drop - No Rule Match
- Packet is dropped

The packet header and payload is not sent through the stages; instead, the parser (a fully P4 programmable parser) creates a Packet Header Vector (PHV) from the packet header. The PHV is also stored in the Packet Buffer (PB). Only the reference to the PHV is used for processing by Ingress/Egress stages. This is done prior to stage 0 in Ingress. The payload stays in PB but is accessible from all stages. Only when a payload needs to be processed by an Arm CPU it is copied from/to PB to/from the Arm memory by a separate DMA engine. This transfer is initiated by a stage in the P4 RxDMA, or P4 TxDMA.