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The primary component of a P4 program is a set of user-defined match action tables. P4 treats all match action tables as generic, leaving the user to add their match-action rules via the control plane. <ref>{{cite web |title=P4-16 Specification |url=https://p4.org/p4-spec/p4-14/v1.0.4/tex/p4.pdf |website=P4 Official Website}}</ref>
====Match-Action processing====
Fundamental to P4 is the concept of '''match-action pipelines'''. Conceptually, forwarding network packets or frames can be broken down into a series of table lookups and corresponding header manipulations. In P4 these manipulations are known as “actions” and generally consist of things such as copying byte fields from one ___location to another based on the lookup results on learned forwarding state. P4 addresses only the data plane of a packet forwarding device, it does not specify the control plane nor any exact protocol for communicating state between the control and data planes. Instead, P4 uses the concept of tables to represent forwarding plane state. An interface between the control plane and the various P4 tables must be provided to allow the control plane to inject/modify state in the program. This interface is generally referred to as the “program API”.
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