2. OpenFlow

What is OpenFlow?

OpenFlow:

• is a communications protocol that gives access to the forwarding plane of a network switch or router over the network.
• enables network controllers to determine the path of network packets across a network of switches.
• allows switches from different vendors — often each with their own proprietary interfaces and scripting languages — to be managed remotely using a single, open protocol.

How does OpenFlow work?

• OpenFlow allows remote administration of a layer 3 switch's packet forwarding tables, by adding, modifying and removing packet matching rules and actions. This way, routing decisions can be made periodically or ad hoc (done for a particular purpose as necessary) by the controller and translated into rules and actions with a configurable lifespan, which are then deployed to a switch's flow table, leaving the actual forwarding of matched packets to the switch at wire speed for the duration of those rules.
• Packets which are unmatched by the switch can be forwarded to the controller. The controller can then decide to modify existing flow table rules on one or more switches or to deploy new rules, to prevent a structural flow of traffic between switch and controller. It could even decide to forward the traffic itself, provided that it has told the switch to forward entire packets instead of just their header.

How is OpenFlow placed in the protocol stack?

The OpenFlow protocol is layered on top of the Transmission Control Protocol (TCP) and prescribes the use of Transport Layer Security (TLS).

What is the standard port for OpenFlow?

Controllers should listen on TCP port 6653 for switches that want to set up a connection.