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What is SD WAN? (2023)

What is SD WAN? (2023)

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The term SD WAN was coined by networking publications as early as 2014. SD WAN stands for "Software Defined - Wide Area Network", a type of overlay network covering OSI Layers 4-7. An overlay network is a virtual network built on top of underlay connectivity. Virtualization and WAN edge devices provide the overlay network with traffic transport independence for the network. SD WAN consists of four planes: Data, Control, Management and Orchestration.

SD WAN is an intelligent WAN (Wide Area Network) providing a direct link between cloud-based applications, branch offices and remote users with dynamic control of traffic pathing for traffic flow optimization. SD WANs provide end-to-end traffic encryption and inspection. Next-gen SASE (Secure Access Service Edge) features are increasingly being added, such as those found in Next-gen security devices, such as botnet intervention and anti-malware systems. This article aims to dispel the myth that SD WAN services are just an expensive broadband link.

How does SD WAN work?

SD WAN uses software to control and manage the interactions between branch and remote user locations and central resources hosted in the headquarters data center. Increasingly enterprises are seeing the benefit of using the public Internet to enable employees to work from any device, anywhere in the world. To facilitate this and provide remote users with secure and reliable access to business-critical resources, many businesses have migrated the majority of applications to be hosted by public cloud service providers such as Google Cloud, Microsoft Azure and Amazon Web Services (AWS).

SD WAN can intelligently and coherently control the path of traffic to optimize traffic flow and choose the best data path transmission. SD WAN technologies also leverage integrated security with real-time cloud intelligence.

What challenges does SD WAN solve?

Top SD WAN Challenges

With rapidly spreading cloud adoption and increasing usage of cloud-based applications, we need ways to simplify the management of Wide Area Networks. SD WAN technology providers and vendors have become increasingly important during the Covid-19 pandemic, with businesses looking to maintain application performance and connect users working from home without sacrificing security.

Traditional WAN utilizes dedicated circuits such as legacy Frame Relay or Multiprotocol Label Switching (MPLS) connections. Frame Relay during the 90s and early 2000s, and later MPLS, were the obvious choices due to the reliability and security provided for application traffic and WAN connectivity to branch offices.

On the other hand, Software Defined WAN is transport-independent, enabling hardware, software clients or virtualization to route application traffic but does not necessarily require networking hardware.

SD WAN uses and functions

SD WAN software monitors the conditions of public and private lines and determines where to redirect application traffic. The default may include sending Voice over Internet Protocol (VoIP) traffic through an MPLS service. In some cases, MPLS connections become congested; the SD WAN might transfer this data to the broadband Internet. In this manner, SD WAN provides automatic load balance and congestion management to optimize performance and minimize costs.

What are the benefits of SD WAN?

SD WAN ensures that there is no need to backhaul traffic. Traffic backhauling is a legacy problem requiring traffic to be backhauled to data centers to utilize inspection and security services. Traffic backhauling can cause delays (latency) and performance issues. SD WAN can easily interact and ensure secure connections with cloud applications such as Office 365 and Dropbox and cloud hosting services such as Amazon Web Services (AWS) and Microsoft Azure.

SD WAN enables network administrators to control the entire network through a centralized management console. As more and more businesses turn to cloud-based storage to improve collaboration and efficiency, Software Defined Wide Area Networks ensure reliable and secure access to cloud resources without degradation of application performance.

SD WAN architecture

Top SD WAN Challenges

SD WAN explained is a paradigm shift from the traditional "walled garden" approach to a much more accessible and more open connection to the public Internet. Many factors can cause performance to fluctuate, such as computer or network configuration or Internet Service Provider (ISP) used. Broadband high-speed transmission technologies such as fiber leased lines and broadband offer faster and always-on Internet access. Leased Lines is a connection to the business directly rented from an ISP providing a dedicated fixed-bandwidth data connection.  An MPLS connection, unlike SD WAN, uses "labels" rather than network addresses to direct data from one node to the next using the shortest path. SD WAN runs across the Internet and multiple transport types (private circuits and MPLS), using an Overlay Management Protocol (OMP) to ensure transport independence. When a Software Defined WAN and MPLS routers are hosted as a hub and spoke in a transit hub site (traditionally a data center) for a hybrid deployment, OMP can redistribute to Open Shortest Path First (OSPF), enabling intelligent routing decisions based on the summary route, choosing the most suitable path to optimize traffic flow.

Now, this can all get quite confusing, and you may still wonder, "but what is SD WAN?" think of SD WAN solutions like any other of your virtual appliances. Neither traditional WAN nor SD WAN has a physical connection. Still, SD WAN has a virtual connection abstracting itself and residing above a physical connection. It is easy to switch between devices or quickly change depending on the needs of the business. Software-defined WANs are virtual architectures that allow companies to leverage multiple connection types or transport services, such as LTE or MPLS, to connect users securely.

SD WAN is primarily based on software-defined networking technologies to create networks. SD WAN focuses on the network management of the network with software controllers hosted within Cloud environments. These include:

  • Data Plane - Can be physical, virtual or hybrid; establishes the network and forwards traffic.

  • Control Plane - Ensures the enforcement of policies. Communicates via an Overlay Management Protocol (OMP).

  • Management Plane - The Graphical User Interface (GUI) for managing the solution, including provisioning, configuration and monitoring.

  • Orchestration Plane - Can provide remote provisioning to any SD WAN-enabled router added to the network form anywhere without needing network administrators to take action. This plane also enables orchestration and "Zero Trust" provisioning.

The control elements establish secure control channels between themselves and each of the WAN edge routers using IPsec tunnels. This ensures the secure provisioning and configuration of devices.


It's changed times, and companies are using cloud technology and integrating SaaS with software. While customers traditionally connect to a corporate data center to access business applications, the cloud provides better access for many applications. In other words, traditional "walled garden" wireless WAN networks have become insufficient for transferring traffic to the cloud, primarily due to latency and poor performance of applications due to the necessity to backhaul traffic to the data center.

Basic SD WAN vs business-driven SD WAN

SD WANs should be as unique as the business that uses them. Software-defined networking opens up plenty of new networking options that are easily wasted. In a basic SD WAN solution, pre-defined rules are usually programmed via templates for traffic steering. In contrast, in a business-orientated SD WAN solution, rules are tuned to business needs steering WAN traffic to ensure optimal application performance at all times under any network condition or change, such as diminished functionality or congestion.

Why should your business choose SD WAN?

Top SD WAN Challenges

For years businesses have looked to Virtual Private Networks (VPNs) and SaaS services instead of improving network infrastructure as a bandaid solution to provide remote users with a secure connection to critical applications. These solutions, however, could be responsible for compromising security.

Whilst VPNs help to prevent man-in-the-middle attacks, however threat actors can compromise the network using other methods, such as by gaining access to physical devices or, more commonly, insider attacks whereby unaware employees open malicious links, providing the attacker with a vulnerability to exploit.

SD WAN offers end-to-end segmentation features that improve network security by limiting resource access across departments. SD WAN deployment is accessible with many SD WAN providers offering solutions with Zero-Touch Provisioning. Zero-Touch Provisioning is ideal for small to medium-sized businesses as using a switch feature; devices can be automatically configured during set-up for rapid deployment of a network device into a large-scale environment reducing the resources and labour required to add the device to the network.

Why SASE security and SD WAN work together?

SD WAN is a fundamental component of Secure Access Service Edge (SASE) security. Since SASE is responsible for the control of Layers 3 and 4, as well as Layer 7 rule definition and IP anonymization, access to the control plane using SD WAN can simplify implementation by minimizing the number of networking vendors used.

A SASE provider that offers SD WAN as part of its solution is already leveraging end-to-end traffic encryption and inspection, improving network security. A SASE solution, native to a particular SD WAN product, can help provide consistent security through data encryption and other SD WAN security functions while minimizing vendor footprint. Why SASE security is necessary is a topic for another time.

However, implementing a unified product is a great way to futureproof your network security whilst reducing the number of points at which problems can arise by using a single provider. Any vendors worth their salt will bundle their network software as part of a broader SASE offering which improves network security with features such as a next-generation firewall.

How SD WAN involves cloud environments?

Although security and reduced traditional WAN costs have been key drivers in the development of Software Defined Networks, rapid and secure integration is an even more significant motivational factor. Several trends have driven an increase in the use of the technology. Among them are the increasing adoption of containers and cloud services. Customers look to SD WAN technology increasingly to link data centers to the cloud.

What is WAN optimization?

WAN optimization (sometimes called WAN acceleration) aims to improve data transfer efficiency across the WAN between an enterprise's dater centers and remote locations. The widespread use of these technologies will increase the speed at which users can access resources, improving the user experience. Measures often used include technologies that increase throughput, reduce latency and packet loss and maximize limited bandwidth.

Where does SD-Branch fit into SD WAN?

A branch of SD WAN is another software technology called SD-Branch, namely software platforms that support SD WAN routing, integrated security and wireless networking and can manage it all centrally. SD-Branch is characterized by operational agility.

The SD-Branch allows enterprises to implement branch-in-a-box solutions in various new locations quickly. They have a central control panel allowing them to manage branch networks and security functions. Reducing or eliminating IT staff visits to a remote site can significantly reduce costs.

How AI is driving advancements in SD WAN Technology in 2023 and beyond

Many see the rise of SD WAN as a curtain call for legacy WAN architecture such as MPLS. The Internet is awash with articles lauding SD WAN as a "magic bullet" or pitting SD WAN against every technology released since 1969. Themes such as "SD WAN Vs < Insert technology here >" fail to mention that, in truth, these are comparisons of where we were to where we are and not a competition but is instead an ongoing process of adapting to developments in connectivity technology.

As technology advances in new and exciting ways, so too does the necessity to adapt our networks to be able to implement it, a job not nearly as glamorous. For the moment, internet traffic increases daily, and engineers seek to ease out every ounce of network bandwidth from their broadband Internet. Even today, we see resources shift away from their traditional home in the data center and into the cloud. SD WAN ensures we adapt and get the most out of these advancements, though MPLS and legacy network architectures will still have their place.

One hot-headed SD WAN question remains whether MPLS' death will be caused by packet-transfer technologies that use labels when deciding on the data transfer. Most typical use cases include branch office campuses, networking, metro Ethernet service, and enterprises needing high QoS (Quality of Service) for real-time applications. Network vendors have believed this will be the end for MPLS for an extended period, but SD WAN cannot eliminate its necessity completely. Gartner says many companies can easily upgrade or replace costly MPLS networks with Internet-based VPNs.

Next on the horizon is the rise of Artificial Intelligence (AI) for the WAN. AI will soon complement the security foundation and rich capabilities of the wide area network SD WAN by leveraging contextualization to provide visibility into WAN end-user experiences with application-based context. AI will enable internet broadband issues to be solved without the need for time-consuming dashboards. Entirely driven by APIs, all security and network operations across all sites can be integrated and automated, providing proactive recommendations on issues impacting the end-user experience.

The key here is the AI's ability to contextualize telemetry data to derive insights that indicate the quality of the user experience. AI will allow faulty interfaces and edge device misconfigurations to be automatically identified and corrected. User impact analysis can be undertaken end-to-end, drawing upon Wired, Wireless and WAN telemetry, events and states to identify application performance issues or other issues such as Dynamic Host Configuration Protocol (DHCP), authentication and Domain Name System (DNS).

What are the best SD WAN Solutions?

The best SD WAN solutions require an in-depth analysis of business requirements, existing network infrastructure, business outcomes, scalability etc. Another vital consideration is managed services, as some providers offer their SD WAN products as Software as a Service (SaaS) solutions. Our Top 10 list of SD WAN providers include both Managed Service Providers and SD WAN vendors, and discover our nomination for the Best Global SD WAN Provider.

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