User Metadata

Simplify Packet Processing Design with P4 and Vivado Tools (WP555)

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User metadata, inferred in the P4 code, provides side-band signaling alongside the packet data at the input to VNP4. It can be processed within the parser and the match-action pipeline, then it is output again alongside the packet data. One common use provides ingress and egress port number information to indicate where each packet is coming from and going to.

Targeting an FPGA or adaptive SoC means that VNP4 has the benefit of being able to scale the side-band signaling to any width to suit each application. The user metadata structure can be broken down into further struct definitions for convenient grouping of fields. It can be defined to align with other standard architectures (such as Portable NIC Architecture), but it is not restricted to any one of these definitions.