Using OpenFlow switches in networks: Glossary Definition
An OpenFlow switch is a network switch based on the OpenFlow protocol that employs software-defined network (SDN) techniques to forward packets in a network.
In an SDN, the packet forwarding function (also known as the data plane) is disaggregated, or decoupled, from the control plane, where routing decisions are made. The data plane is implemented in the OpenFlow switch, but takes packet forwarding instructions from a separate SDN controller, which makes all routing decisions.
This is a departure from traditional network switches, which have packet forwarding capabilities and routing intelligence built into each switch. What’s more, traditional switches run a network operating system that is proprietary to whatever vendor sells that switch, so customers are effectively forced to buy all their networking equipment from the same vendor.
OpenFlow is intended to enable an open source network architecture. It is managed under the auspices of the Open Networking Foundation, a non-profit consortium that is “building solutions by leveraging network disaggregation, white box economics, open source software and software defined standards,” according to its website.
Decoupling the data plane from the control plane brings a number of benefits to carrier, data center and enterprise networks, including improved traffic management capabilities. Traditional network infrastructure devices use routing protocols such as TCP/IP and relatively static access control lists (ACLs) on routers to determine how to route packets in a network.
An OpenFlow switch uses flow tables and a group table to perform packet lookups and forwarding. Each SDN switch communicates with the SDN controller using the OpenFlow protocol. The controller can add, delete or change entries in the flow tables in response to packets or on its own, proactively, due to network conditions. In that sense, it can make far more dynamic routing decisions based on a combination of factors, including predefined policies and the conditions in the network at any given time.
For example, an SDN controller could take advantage of routes that are under-utilized to handle non-critical traffic, and implement load balancing by directing traffic to different servers. It can improve security by mirroring any port to a network monitoring device, without limiting performance, and more easily create virtual LANs (VLANs).
OpenFlow switches are also a natural fit for white box networking, where the network operating system is disaggregated from the underlying network hardware. White box networking enables companies to use commodity hardware and ASICs – white box switches – from the same companies that supply switches to major router vendors, but install an open NOS on top, including an OpenFlow-compatible NOS. This enables companies to build an open network that has the same or better performance as a traditional network but is far less costly up front in terms of capital costs and in terms of long-term operational costs.
Pica8’s PICOS, for example, is an OpenFlow-compatible NOS that runs on a range of white box switch hardware. It enables an enterprise to choose the hardware that best fits their price/performance requirements while preserving their option to upgrade the switch hardware as newer models come along – and simply porting the NOS to the new switch platform.