OpenFlow: Creating a solid foundation for software-defined networking

BANGALORE, INDIA: Traditional networks and data centers are being stretched to their limits. They were never designed for today's astronomical growth in bandwidth-intensive applications-and the ever-increasing demand for speed, scalability, and resilience.

Software-Defined Networking (SDN) is a powerful new network paradigm designed to address these issues. SDN is considered the technology that will revolutionize the networking industry in the next few years. The main advantage is an increase in agility and flexibility, not to mention cost savings.

The SDN approach allows the effective use of network resources and is particularly useful for applications such as VM (Virtual Machine) Mobility, mission-critical networks and IP-based mobile networks. OpenFlow is the pre-requisite for this paradigm shift

OpenFlow is an emerging, industry-standard SDN communications protocol that provides access between the forwarding plane of a network switch or router and a network controller, facilitating more sophisticated traffic management and engineering. OpenFlow provides greater programmatic control of the network, enabling new network applications to be developed for virtualized environments.

On the market there are routers and switches with different programmability - and therefore planning and management of traffic becomes a problem due to inconsistency between the equipment of different suppliers within the data center. OpenFlow remedies this issue. The independence of the supervisory function of the controlled hardware makes planning and management of traffic consistent.

OpenFlow originated out of Stanford University. They tried to find an open standard for research; a way to run experimental protocols over existing campus networks, thus facilitating innovation.

Today OpenFlow has been further developed and adopted by network providers and used in many large scale enterprise networks. It is added as a feature to commercial Ethernet switches, routers and wireless access points - and provides a standardized hook to allow researchers to run experiments, without requiring vendors to expose the internal workings of their network devices.

But how does OpenFlow Work?

In a classical router or switch, the fast packet forwarding (data path) and the high level routing decisions (control path) occur on the same device. An OpenFlow Switch separates these two functions. The data path portion still resides on the switch, while high-level routing decisions are moved to a separate controller, typically a standard server.

The OpenFlow Switch and Controller communicate via the OpenFlow protocol, which defines messages, such as packet-received, send-packet-out, modify-forwarding-table, and get-stats. The data path of an OpenFlow Switch presents a clean flow table abstraction; each flow table entry contains a set of packet fields to match, and an action (such as send-out-port, modify-field, or drop).

When an OpenFlow Switch receives a packet it has never seen before, for which it has no matching flow entries, it sends this packet to the controller. The controller then makes a decision on how to handle this packet. It can drop the packet, or it can add a flow entry directing the switch on how to forward similar packets in the future.

The hybrid approach

With hybrid port mode, OpenFlow is able to integrate and run on the same physical infrastructure as traditional routing and switching. This unique capability provides a pragmatic path to SDN by enabling network operators to maximize the value of their network. It gives them the programmatic control offered by SDN for specific flows while the remaining traffic is routed as before, and it is possible to scale up the OpenFlow deployment as network demands change.

Specifically, this means that potential customers can operate their traditional network parallel to an OpenFlow network. The traffic can flow between the networks without having to go through a switch. The result: lower costs, because each port in the switch costs a certain amount.

The cost of enabling OpenFlow is drastically reduced, since a network manager can use OpenFlow without interrupting the traffic on the existing network. Configuration time is drastically reduced since OpenFlow can be as easily activated as enabling IPv6 in Windows 7.

OpenFlow is thus the basic foundation for Software-Defined Networking (SDN), enabling organizations to realize huge savings without major investment and at the same time bringing flexibility to the network infrastructure.

Samer Ismair is network consultant, MEMA at Brocade Communications