Software-Defined Wide Area Networking (SD-WAN) Fact Sheet

What is SD-WAN? What are the pros and cons of SD-WAN? Do you need a middle-mile network and/or underlay circuits? This SD-WAN fact sheet covers it all.

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Rob Rodier

Jan 26, 2022


For many prospective buyers, Software Defined Wide Area Networking (SD-WAN) can be an especially difficult technology to grasp. 

SD-WAN makes the public Internet a node on the enterprise WAN, a notion that enthralls with the potential of more affordable and flexible transport as much as it concerns with all the management complexity that it may entail. 

It also comes in a variety of flavors and combinations - both operator-managed and self-managed - sometimes with the potential for middle-mile management and different levels of security capabilities. 

This post provides a quick reference fact sheet to those looking to understand SD-WAN.

What is SD-WAN? 

SD-WAN is a software-based architecture that acts as a virtual overlay to an underlying hardware-based network, and provides a centralized control function to efficiently steer traffic across a WAN based on an enterprise’s business needs. 

By enabling traffic prioritization, SD-WANs can support many of the same quality of experience and security benefits of MPLS or P2P for important applications, but with data transmission occurring, for the most part, over the public internet rather than on preset or dedicated routes. A key difference when comparing SD-WAN vs MPLS is that SD-WAN acknowledges the public internet as arguably the most important node on the enterprise WAN. SD-WAN’s reliance on the internet is why many people think it is a cheaper WAN option than dedicated circuits (more on that later).

An important distinction to make is that other WAN options rely on having their own physical form of transport while SD-WAN does not. SD-WAN provides a decoupling from the physical underlay network,  allowing it to be completely vendor agnostic, while software manages the overlay network essentially as an intelligent VPN (see this post on SD-WAN vs VPN). However, in many cases SD-WAN’s overall quality is only going to be as strong as that of the underlying network on which it rides..

Even with SD-WAN as an option, underlying dedicated internet access circuits continue to be important for supporting services governed by service level agreements or requiring some form of service performance guarantee. See this post on why quality circuits still matter with SD-WAN for further intel on that topic. 

Still have questions on SD-WAN? Check out this resource next: SD-WAN for Dummies: The Ultimate Buyer's Guide

Pros & Cons of SD-WAN

Pros of SD-WAN

  • Cost reduction can be achieved through leveraging of the public internet and the ability to remain transport network-agnostic.

  • It improves business agility and ability to scale an enterprise’s facilities footprint without reliance on dedicated transport.

  • Software overlays provide intelligent network management and granular reporting of performance, application utilization, top talkers, etc.

  • SD-WAN is designed for increased reliance on cloud services oftentimes with dedicated peering into major public cloud and SaaS platforms.

  • The ability to massage traffic, perform error correction and set priority queues for traffic improves overall quality.

  • API integrations on many platforms enable custom integrations, reporting and monitoring.

  • Enterprises can still take advantage of vendor-level guarantees of consistent user experience.

  • It can be paired with SASE and other security options to ensure service protection.

If you're intrigued by the benefits of SD-WAN but currently feel "stuck" on your MPLS network infrastructure, check out this guide to Transitioning from MPLS to SD-WAN!

Cons of SD-WAN

  • The SD-WAN market is a fragmented landscape, and the service may provide less certainty on performance metrics vs. MPLS/P2P.

  • Despite the power of SD-WAN, the overlay still needs quality underlay circuits for optimal performance. 

  • If you need to transmit large amounts of data (10Gbps +) between multiple sites and latency is of the utmost importance for your business, then you might not want to utilize SD-WAN - ultra high bandwidth requirements are where you start to see the cost/benefit of SD-WAN tipping in the wrong direction.  

  • Because it technically uses the public internet in many cases, SD-WAN may raise security concerns for some customer profiles. However, modern SD-WANs can be encrypted to such a level so that this is no longer a concern (check out the 256-bit encryption VMware offers). 

Key Decisions When Evaluating SD-WAN 

As with most technology implementations, there are different approaches and deployment models for SD-WAN, and any enterprise looking to adopt the technology will be faced with several choices to make:

Do you want to self-manage your SD-WAN service and appliances, or have another company manage them for you? 

All SD-WAN services rely on edge appliances, which an enterprise can configure and manage itself, making all the decisions and adjustments regarding the traffic and applications to be prioritized. This keeps the upfront deployment cost relatively low, though may require more long-term investment in hiring and retaining skilled IT staff. Under a managed service, another provider takes care of all that for an ongoing subscription fee.

If you want a managed SD-WAN service, do you want middle-mile SD-WAN platform support as part of that solution? 

SD-WAN platforms with their own middle-mile network can offer other quality of experience capabilities and security features packaged along with the SD-WAN service. For example, a middle-mile provider will create a VPN tunnel from their edge appliance to the nearest available point of presence (PoP) on their middle-mile network.  All of the traffic from the edge device will then traverse that middle-mile network where it can then be routed more predictably and efficiently to its final destination. This is irregardless of whether that destination is another public cloud, or private node on the corporate WAN. 

As such, SD-WAN providers that operate middle-mile networks can provide greater levels of resiliency and predictability, while also offering additional services like Unified Communications as a Service (UCaaS) or Secure Access Service Edge or Zero Trust security.

Do you want a managed service provider with its own underlay network?? 

When procuring an SD-WAN overlay network, the provider will likely assume that you already have your underlay network in place or are procuring the underlay circuits in tandem. For a customer who desires a “single throat to choke” for both their underlay physical connectivity network and their SD-WAN overlay they may opt for a MSP or pure play SD-WAN provider that also manages all aspects of the physical underlay network. 

For a deeper dive on how to select an SD-WAN provider, check out this blog next: What to Consider when Comparing Managed SD-WAN Providers

Hope this was helpful!

We hope you enjoyed this SD-WAN fact sheet.

If your company is considering making the switch to SD-WAN, try Lightyear’s 2-minute online questionnaire to kick off the procurement process. Our software has automated the telecom service procurement process and will manage your implementations for you, as well!

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