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How SD-WAN Works

We’ve all heard this saying: “Good, fast or cheap. Pick any two.” With software-defined WAN (SD-WAN), you can get all three. SD-WAN enables a more agile, manageable and secure network, with greater performance at lower cost. 

How SD-WAN Works

Legacy WAN architectures rely on dedicated circuits and proprietary hardware, creating a network that’s inflexible and difficult to manage. As organizations move workloads to the cloud and look to connect remote locations, the traditional WAN quickly becomes unworkable. SD-WAN overcomes the limitations of traditional WAN technologies to better support today’s business and IT requirements.

SD-WAN applies the principles of software-defined networking (SDN) to the wide-area network. SDN separates control of the network from the devices themselves so that software can be used to route traffic in response to changing network conditions. A centralized controller tells the routers and switches where to send data packets according to defined policies.

The value of this software layer cannot be overstated. It creates a virtual network overlay that provides path selection across multiple WAN connections based upon network conditions and application requirements. It also supports additional services such as WAN optimization and firewalls, all of which are fully controlled by a centralized application.

IT and Business Value

Historically, IT managers have preferred multiprotocol label switching (MPLS) for enterprise WANs due to its inherent reliability. Broadband Internet, in contrast, provides only “best-effort” delivery. However, SD-WAN can aggregate multiple links in an active/active configuration, creating a highly reliable network that significantly reduces the risk of downtime. Policy-based routing features also enable automatic failover to a backup circuit in the event of a service provider outage.

SD-WAN allows for more flexible deployment options and faster provisioning of WAN services. Administrators can manage the entire network from a single console and gain the visibility needed to troubleshoot problems rapidly.

SD-WAN also provides greater security through built-in VPN capabilities. Best-in-class solutions integrate next-generation firewall, intrusion detection and prevention, content filtering and malware protection.

Improved Performance

It’s natural to assume that MPLS, which functions like a dedicated circuit, would have a performance edge over SD-WAN. However, MPLS performance depends on the routing policies of the service providers and network interconnects. 

SD-WAN allows administrators to prioritize certain traffic, such as voice, video and other latency-sensitive applications, according to business needs. It also addresses network congestion, packet loss and packet delay to ensure high-quality IP communications. 

What’s more, SD-WAN streamlines cloud access. Traditional WANs typically backhaul all traffic — including cloud traffic — from branch locations through the security controls at headquarters. This creates latency that can impact application performance. SD-WAN fully supports SaaS applications and software hosted in public and private clouds, delivering a high-quality user experience while protecting the organization from threats.

Cost Savings

SD-WAN enables organizations to cut costs significantly. The primary savings comes from leveraging cost-efficient broadband Internet services in lieu of MPLS. SD-WAN can also reduce capital expenditures on equipment and management overhead.

Because SD-WAN allows for the virtualization of WAN and security services, there’s no longer a need for the traditional “branch stack.” Everything can be collapsed onto a single SD-WAN appliance and managed centrally through a cloud-based interface. Additionally, SD-WAN provides automation and orchestration tools that handle many aspects of provisioning, policy development and administration.


SD-WAN delivers greater reliability, flexibility and security, with the performance needed to support today’s latency-sensitive and cloud-based applications. It also helps reduce telecom costs and administrative overhead. The networking experts at Rahi are here to help you evaluate SD-WAN and determine how it can benefit your IT environment.

Tim Haney

Tim is a senior network engineer for Rahi, with more than seven years of experience. He holds about 35 active certifications in networking technologies.