What Is Software-Defined Wide Area Networking (SD-WAN)?

SD-WAN provides a secure path from siloed enterprise networks to the public, private and hybrid cloud

SD-WAN is a reset in thinking about how a Wide Area Network (WAN) should work. It’s a virtual WAN architecture, an overlay that can work with different network transport services, including broadband. SD-WAN enables organizations to centrally manage traffic using the principles of Software Defined Networking (SDN), without the limitations imposed by physical network infrastructure. 

SD-WAN centralizes network control, management, provisioning and security, despite the continued decentralization of data, as businesses move to the cloud. A few companies stand apart from the rest when it comes to offering SD-WAN solutions. Cisco is the market leader, followed by Fortinet and VMware, according to a report from Dell’Oro Group.

Enterprise spend on SD-WAN has accelerated in recent times. Businesses are upgrading network infrastructure to accommodate changing objectives and shifting workforce demands, as well. Sales of SD-WAN solutions rose 45% year-over-year for the third calendar quarter of 2021, according to Dell’Oro. The research firm noted that Cisco’s quarterly SD-WAN revenue nearly doubled in the quarter, with especially strong growth in North America. 

The State of the WAN

For years, the literal backbone of enterprise WAN connectivity has been Multi-Protocol Label Switching (MPLS). MPLS is a routing technique which directs data based on short path labels rather than long network addresses. Those paths labels speed network traffic by identifying virtual links between distant network nodes, eliminating routing delays.

MPLS supports a range of network transport services. And as the acronym implies, it supports multiple networking protocols: Internet Protocol (IP), Asynchronous Transport Mode (ATM) and Frame Relay, for example. 

Regardless of protocol, MPLS connections all have one thing in common: They’re dedicated circuits, and require specialized routing hardware at both ends. This complicates provisioning and limits scale. What’s more, traditional WAN topologies typically backhaul all network traffic for security. This creates bottlenecks and complicates network traffic management.

A WAN topology that restricts the flow of network traffic to the cloud is at direct odds with enterprise digitalization strategies. Enterprises depend on more cloud-based services than ever to manage essential business functions. SaaS platforms like Customer Relationship Management (CRM) and Enterprise Resource Planning (ERP) are examples. These platforms provide organizations with agility, flexibility, and scale, but being cloud-native demands a new approach when it comes to practical network management. 

SD-WAN modernizes network operations for the cloud

As enterprises and users turn to the cloud, the difference between data center cloud and public cloud can get nebulous. Increasing public cloud-dependence and adjacency introduces complications to network security and compliance. Data sovereignty, compliance and security is top of mind for every IT professional.

Many enterprises leaning into to the cloud are implementing Software-Defined Wide Area Networking (SD-WAN) to manage their networks. SD-WAN abstracts the networks’ transport service altogether. It’s a virtual WAN architecture which enables organizations to leverage whatever transport service they need — broadband, MLPS, 4G LTE, 5G. 

By separating the network’s control plane altogether, SD-WAN enables businesses to centralize network management, security, and provisioning. SD-WAN replaces dedicated network hardware with Virtual Network Functions (VNFs) in place of physical networking hardware. 

VNFs specifically replace devices like network routers and firewalls. VNFs are implemented as Virtual Machines (VMs) which run as software in the IT cloud, operating on commercial off-the-shelf (COTS) server hardware. Accompanied by Cloud-native Network Functions (CNFs), they provide IT departments with the ability to scale services instantly to meet demand. As software rather than hardware, VNFs and CNFs can be continuous updated and optimized.

While VNFs are nothing new to enterprise IT, what’s new here in the SD-WAN equation is how SDN itself helps IT operations manage network operations and data security for branch and remote locations. There are some key differences, too. 

“SDN advocates a central controller to dictate network behaviors. In contrast, SD-WAN generally manages based on central policy control, but decisions may also be made locally while taking into consideration the corporate policies. Or decisions can be made centrally while incorporating knowledge of local conditions reported by remote network nodes,” said VMware.

SD-WAN in the wild

SD-WAN has emerged as an opportunity for carriers and hyperscalers, Over-the-Top (OTT) service providers, and edge services. In December, Amazon introduced AWS Cloud WAN as a way to replace what it called a “patchwork” of services needed to handle private network control and management. AWS Cloud WAN connects on-prem data centers, branch offices and cloud resources together on AWS’ global backbone, consolidating management through a central dashboard. 

Verizon features SD-WAN managed by Cisco as an option for its Network as a Service (NaaS). It comprises Cisco Umbrella security framework, manages zero trust application access and provides managed services through Cisco products including Pluggable Interface Modules and Catalyst Cellular Gateways.