Scalable Programming for SDN Controllers

Introduction. A major recent development in computer networking is the notion of Software-Defined Networking (SDN), which allows a network to customize its behaviors through centralized policies at a conceptually centralized network controller. In particular, Openflow [4] has made significant progress by establishing (1) flow tables as a standard data-plane abstraction for distributed switches, (2) a protocol for the centralized controller to install forwarding rules and query state at switches, and (3) a protocol for a switch to forward to the controller packets not matching any rules in its switch-local forwarding table. This progress has provided critical components in realizing the vision that a network operator configures a network by writing a simple, centralized network control program, with a global view of network state, thus decoupling the program from the complexities of managing distributed state. We refer to the programming of the centralized controller as SDN programming, and a network operator who conducts SDN programming as an SDN programmer, or just a programmer. A critical component in realizing the full benefits of SDN is the SDN programming model, through which a programmer defines its network behaviors. Existing programming models require either explicit or restricted declarative specification of flow patterns, introducing a major source of complexity in SDN programming. In this project, we explore an SDN programming model that enables an SDN programmer to apply a high-level algorithmic approach to define network-wide forwarding behaviors of network flows. Specifically, the programmer simply defines a function f , expressed in a general-purpose, high-level programming language, which the centralized controller conceptually runs on every packet entering the network. When designing the function f , the programmer does not need to adapt to a new programming model but uses a standard programming language to design arbitrary algorithms to classify input packets and return a network-wide forwarding path describing how each packet should be forwarded to organize traffic. We refer to this model as SDN programming of algorithmic policies. We emphasize that algorithmic policies and declarative policies do not exclude each other. Our system supports both, but this paper focuses on algorithmic policies.