What is SD-WAN: Software Defined WAN

SD-WAN, Software Defined Wide Area Network is a form of networking technology where the networking hardware is decoupled from its control mechanism

Data Networking Fundamentals Includes:
Networking fundamentals     Local area networks    

See also: Software defined networks     Network functions virtualisation     SD-WAN    

SD-WAN stands for Software Defined Wide Area Network, and it is a networking technology which is finding more popularity and use within the telecommunications industry.

SD-WAN is a virtual WAN technology that allows enterprises to utilise and combine a variety of different transport services including MPLS, broadband services, mobile communications including 4G LTE and 5G, etc. This is achieved within a secure environment that allows users to connect to their applications.

The concept of SD-WAN uses centralised control to enable the data traffic to be routed across the wide area network intelligently and securely. This increases the efficiency and performance, improves the user experience, and also reduces cost for a given level of performance.

Reason for SD-WAN

A huge amount of data networking these days involves Cloud technology: Cloud storage, Cloud computing, and the like. This means that any wide area network technology needs to operate in a fashion that can interface easily to the cloud.

Traditional WANs that are based on technology using traditional routers do not easily lend themselves to Cloud usage as the system needs to be particularly flexible dependent upon the way of working, the application and the like.

Additionally, much of today's working requires multiple destination points, and this also cannot be accommodated so easily with traditional network topologies.

Traditional approaches often require all traffic, including that destined for the Cloud or anywhere for that matter to be routed via a hub where security inspection, etc can be undertaken. This introduces delays and network bottlenecks, etc.

It is far more efficient to use a flexible software defined WAN approach as this is able to provide the security and other features required as well as supporting Cloud working. SD-WAN can support applications hosted in on-premise data centres, public or private clouds and SaaS solutions.

How does SD-WAN work?

Rather than incorporating a hub through which the data in the wide area network passes, the SD-WAN decouples the networking hardware from the control, so that efficient routing of the data can take place dependent upon the destinations, applications and the like.

An SD-WAN uses a centralised control capability to intelligently steer data across the network. This is based upon a variety of criteria including: priority, quality of service and security.

This compares with the established router-centric approach that distributes the control function across all devices in the network. The routers stored the destination addresses and route the traffic based on TCP/IP addresses and ACLs, Access Control Lists.


There are many similarities between SD-WAN and SDN, but the two technologies are very different. The table below summaries the differences between the two.

SD-WAN is deployed in branch offices as well as in data centres. SDN is deployed in data centres.
The control and data forwarding planes are separated. The control and data forwarding planes are separated.
Off-the-shelf x86 appliances – physical, virtual, cloud. Specialised switching hardware is required.
Centralised control and orchestration but also has zero touch provisioning. Centralised control and orchestration.
New technology but being rapidly adopted. The technology has taken time to mature and be fully introduced.

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