State4: State-preserving Reconfiguration of P4-programmable Switches.

To cater to constantly changing network needs, enabling stateful reconfiguration of Network Functions (NFs) is crucial. Recently, there has been growing interest in offloading NFs to programmable network devices. Unfortunately, it is currently not possible to maintain the full state of NFs during a switch reconfiguration without consuming network resources from and to neighboring switches. In this paper, we present State4, a framework that maintains the state of P4 programs during the reconfiguration of a P4-programmable network device, by only using a small amount of local resources on the switch undergoing reconfiguration. State4 acts on both the inswitch control-plane and the data-plane. By utilizing the in-switch local controller, State4 requires no external network resources to achieve reconfiguration while preserving states. As such, State4 enables on-the-fly reconfiguration of stateful NFs, at minimal traffic disruption, where previously traffic had to be re-routed.