2nd P4 Workshop by Stanford/ONRC

Introducing support for states into the forwarding abstraction of the SDN data plane has recently attracted the interest of the research community. It allows programmability of dynamic forwarding behaviors at data plane with the goal of offloading from the controller to switches the execution of simple state machines based on local events. In 2014, we proposed OpenState as an extension to OpenFlow allowing packets to be forwarded on the basis of "flow-states", maintained by the switch, and updated on the fast path itself as a consequence of packet-level events (flow table match) and timers. We also validated the approach by developing a FPGA-based hardware prototype and several applications based on the new stateful abstraction. In the last two years we have acquired quite some experience on the issues involved in the support of dynamic forwarding behaviors, also within the European project BEBA (Behavioral Based Forwarding) that involves several idustrial partners. Based on this we have worked on a first attempt to use P4 to define an OpenState-like pipeline. We have defined a reusable “openstate.p4” library that developers can use for the implementation of application-specific stateful pipelines. In this presentation we show the basic characteristics of openstate.p4 and an example of application and pipeline related to a fast (1-2ms) port failure detection scheme and automatic routing failover. This allows us to point out the lessons learned from this first attempt. While P4 already offers basic support to stateful forwarding, we spot few critical issues that are currently not addressed in the specification that are related to timeouts resolution, flow-states indexation, and state coherency when using parallel processing at data plane. We propose ideas for the evolution of P4 in order to address the aforementioned issues and let developers fully exploit the benefits of a stateful (behavioural) data plane.