The SDN controller is interfaced with the hardware of the network (i.e., with switches and routers) using OpenFlow. Basically, OpenFlow is an open interface used for configuring the forwarding tables of network switch according to the desired path derived by the SDN controller. OpenFlow enables more innovation in controller platforms and applications, and describes a solution for each frame or packet flow. OpenFlow is based on an ethernet switch with an internal flow-table and a standardized interface to add and remove flow entries of forwarding table of the system. The control mechanism from each one of the switch and router up to SDN controller are encrypted with the transport layer security (TLS) and secure socket layer (SSL) OpenFlow protocols to provide the additional security inside the network.
TopIntroduction
Open Network Foundation (ONF) defines OpenFlow as
OpenFlow is the first standard communication interface defined between the control and forwarding layers of an SDN architecture. OpenFlow allows direct access to manipulation of the forwarding plane of network devices such as switches and routers, both physical and virtual (hypervisor-based). (Noyes, 2009)
OpenFlow is the initially institutionalized interface and the most commonly used protocol outlined particularly for SDN. It is an open convention used for the communication between controllers and switches. In other words, it is an open interface used for configuring the forwarding tables of network switches and routers according to the desired path of network packets derived by the SDN Controller. In an OpenFlow, surrounding devices which want to communicate to an SDN Controller should support the OpenFlow protocol. OpenFlow uses Transmission Control Protocol (TCP) means that a controller can interact with switch over a network and need not to be co-located at the side of switches. Across this convention, the SDN Controller drops changes to the flow-table of switches/routers which helps network administrator in controlling the flow of packets, splitting the traffic for optimum performance, and are convenient for testing new configurations and applications. Through this, routing paths can be updated time-to-time or ad hoc by the controller and converted into rules and actions with a configurable lifespan, which are then updated to the switches forwarding table, jilting the actual flow of matched packets to the buffer of switch for the time span as per those rules.
The major component of OpenFlow which shares common objective with SDN are:
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Decoupling of the control and data planes of the switches, the control plane is managed by the centralised controllers which may be one or more in number but synchronized.
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Using an institutionalized interface communication between SDN controller and the switches for updating the forwarding table of switch over the network.
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The centralised controllers will be programmed via modern, extensible API's over the network.
The control mechanism of OpenFlow are encrypted with the Transport Layer Security(TLS) and Secure Sockets Layer(SSL) OpenFlow Protocols from SDN Controller to each switch and router to provide the auxiliary security inside the Network. Also, Open Flow allows the controller to remotely manage switches. These switches may have origins from different vendors, with each one of them having its own proprietary interfaces and scripting languages.
TopArchitecture
The key components of the OpenFlow model, as shown in Figure 1, have become at least part of the common definition of SDN, mainly: