Wednesday, December 12, 2012

SDN Architecture - Protocols & Components

Saro Velrajan December 12, 2012 SDN/NFV

Software Defined Networking (SDN) architecture decouples the control plane from the data forwarding plane. SDN architecture provides more programmability and control to the network administrators without requiring physical access to the network's hardware devices. The control plane function is typically centralized. This article describes the SDN protocols and the various SDN components involved in a SDN-ized network.

Also read: SDN Architecture

SDN Protocols

OpenFlow is the most popular protocol used in Software Defined Networks (SDN). However, there are other protocols such as ForCES, PCE, OpenConfig and NetConf used in the SDN world for managing network devices.

SDN architecture consists of a OpenFlow Controller and one or more OpenFlow switches/routers. In an OpenFlow enabled architecture - there are two distinct functions / components - the OpenFlow Controller and the OpenFlow Switch.

SDN Components

OpenFlow Controller

OpenFlow Controller is the control plane application which provides control and visibility into the OpenFlow Switches. It is primarily used for managing the flows and for defining/downloading policies to the network. You can find some open source OpenFlow Controllers (C++ and Python implementations) at http://www.noxrepo.org/. You can also look at the list of OpenFlow controllers in the market

OpenFlow Switch

OpenFlow switches are routers/switches that support OpenFlow protocol. OpenFlow switches can be running on a hardware directly or on a virtual machine. OpenFlow switches forward packets and handles flows based on the programming done by the OpenFlow controller.

An OpenFlow Switch consists of one or more flow tables and a group table, which perform packet look-ups and forwarding, and an OpenFlow channel to an external controller. Using the OpenFlow protocol, the controller can add, update, and delete flow entries in flow tables, both reactively (in response to packets) and proactively. Each flow table in the switch contains a set of flow entries; each flow entry consists of match fields, counters, and a set of instructions to apply to matching packets.