While OpenFlow has received a considerable amount of industry attention, it is worth mentioning that the idea of programmable networks and decoupled control plane (control logic) from data plane has been around for many years. The Open Signaling (OPENSIG) working group initiated a series of workshops in 1995 in order to make ATM, Internet, and mobile networks more open, extensible, and programmable. Motivated by these ideas, Internet Engineering Task Force (IETF) working group came up with General Switch Management Protocol (GSMP) to control a label switch. This group officially concluded and GSMPv3 was published in June 2002.

The active network initiative proposed the idea of a network infrastructure that would be programmable for customized services. However, the active network never gathered critical mass, mainly due to the practical...

The SDN switch (for instance, an OpenFlow switch), the SDN controller, and the interfaces are present in the controller for communication with forwarding devices, generally southbound interface (OpenFlow), and northbound interface (the network application interface), which are the fundamental building blocks of an SDN deployment. Switches in an SDN are often represented as basic forwarding hardware accessible via an open interface, as the control logic and algorithms are offloaded to a controller. OpenFlow switches come in two varieties: pure (OpenFlow-only) and hybrid (OpenFlow-enabled).

Pure OpenFlow switches have no legacy features or onboard control and completely rely on a controller for forwarding decisions. Hybrid switches support OpenFlow in addition to traditional operation and protocols. Most commercial switches available today are...

The communication between the controller and switch happens using the OpenFlow protocol, where a set of defined messages can be exchanged between these entities over a secure channel. The secure channel is an interface that connects each OpenFlow switch to a controller. The Transport Layer Security (TLS) connection to the user-defined (otherwise fixed) controller is initiated by the switch with its power on. The controller's default TCP port is 6633. The switch and controller mutually authenticate by exchanging certificates signed by a site-specific private key. Each switch must be user-configurable, with one certificate for authenticating the controller (controller certificate) and the other for authenticating to the controller (switch certificate). Traffic to and from the secure channel is not checked against the flow table; therefore, the switch must...

External management systems or network applications (Net Apps) may wish to extract information about the underlying network or control an aspect of the network behavior or policy. Additionally, controllers may find it necessary to communicate with each other for a variety of reasons. For instance, an internal control application may need to reserve resources across multiple domains of control, or a primary controller may need to share policy information with a backup controller.

Unlike controller-switch communication (that is, the southbound interface), currently, there is no accepted standard for the northbound interface and they are more likely to be implemented on an ad-hoc basis for particular applications.

A potential reason is that the northbound interface is defined entirely in the software, while controller-switch interactions must enable the...

OpenFlow is the continuation of many previous efforts to provide decoupled control and data forwarding in networking equipment. A background of these efforts was presented in this chapter. Presenting the key building blocks of an SDN deployment, in particular, the OpenFlow protocol and its basic operation were covered in this chapter.

After introducing OpenFlow, in the next chapter, we present the reference implementation of OpenFlow switch in software and hardware, along with an introduction to the Mininet experiment environment.