Advanced Computer Networks

Programmable data plane (P4)

All network features are centered around the capabilities of the ASIC, and it takes years for a new one to be developed and deployed. So, make the ASIC programmable, and let your features tell the ASIC what to support.

PISA: protocol independent switch architecture

P4: domain-specific language for programming protocol-independent packet processors

Architecture specific constructs

• each architecture defines “externs” - blackbox functions whose interface is known
• P4 aims to be target-independent

P4 is C-like, statically typed.

Parser:

• uses state machine to map packets into headers and metadata
• transition statements move between states, with final accept/reject states

Control:

• tables: match a key and return an action
• actions: like C functions
• control flow is similar to C, but no loops

Deparser assembles the packet from data structures.