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software-defined networking (SDN)

Software-defined networking (SDN) is an approach to networking in which control is decoupled from the physical infrastructure, allowing network administrators to support a network fabric across multi-vendor equipment.

 

Software-defined networking (SDN) is an umbrella term encompassing several kinds of network technology aimed at making the network as agile and flexible as the virtualized server and storage infrastructure of the modern data center. The goal of using an SDN architecture is to allow network engineers and administrators to respond quickly to changing business requirements. In a software-defined network, a network administrator can shape traffic from a centralized control console without having to touch individual switches, and can deliver services to wherever they are needed in the network, without regard to what specific devices a server or other device is connected to. The key technologies are functional separation, network virtualization and automation through programmability.

Originally, SDN focused solely on separation of the control plane of the network, which makes decisions about how packets should flow through the network from the data plane of the network, which actually moves packets from place to place. When a packet arrives at a switch in the network, rules built into the switch's proprietary firmware tell the switch where to forward the packet. The switch sends every packet going to the same destination along the same path -- and treats all the packets the exact same way. In a classic SDN deployment, rules for packet handling are sent to the switch from a controller, an application running on a server somewhere; switches (aka data plane devices) query the controller for guidance as needed, and provide it with information about traffic they are handling. Controllers and switches communicate via a controller's "south-bound" interface, usually a protocol called OpenFlow, although other protocols exist.  

software defined networking (SDN), software-defined networking diagram

Where a conventional network would use a specialized appliance like a firewall or load balancer, a software-defined network deploys an application that uses the controller to manage data plane behavior. Applications talk to the controller via its "northbound" interface. As of the end of 2014, there was no formal standard for the application interface of the controller to match OpenFlow as a general southbound interface. The OpenDaylight controller's northbound API may emerge as a de facto standard over time, given its broad vendor support.

The administrator can change any network switch's rules when necessary -- prioritizing, deprioritizing or even blocking specific types of packets with a highly granular level of control. This is especially helpful in a cloud computing multi-tenant architecture because it allows the administrator to manage traffic loads in a flexible and more efficient manner. Essentially, this allows the administrator to use less expensive commodity switches and have more control over network traffic flow than ever before.

This was first published in May 2015

Next Steps

Read more about the Open Networking Foundation’s role in SDN

Learn more about the features of the Brocade VDX 8770 switch series, including support for OpenStack and SDN technologies.

Get an overview of the Cisco Nexus 9500 data center-class switch series, which supports Cisco's software-defined networking strategy.

Learn about the Dell E-series of data center-class switches.

Learn more about the HP FlexFabric 12500 data center-class switch, which supports the OpenFlow 1.3 protocol.

A breakdown of capabilities and features of the HP FlexFabric 12900 data center class switch series, such as SDN implementation support.

Juniper EX9200 data center-class switches are SDN-friendly with support for technologies like OpenStack. Learn more here.

Learn about the Cisco Nexus 7700 switch series.

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