The CIOs Guide to SD-WAN

Building the case for a faster, better, and cheaper network

Executive Summary

SD-WAN is a potential game-changer for wide area networking—on the same level as server virtualization, which transformed data centers over the last 10 years. SD-WAN combines the use of multiple active branch links, intelligent direction of traffic across those links, and centralized, policy-driven management of the WAN as a whole. The ability to leverage multiple lower-cost services (including Internet and 4G wireless) as well as traditional services like MPLS holds the promise of transforming IT’s relationship to the WAN and the WAN’s relationship to the business.

Transformational potential is not enough. IT has to build a compelling business case for making the transition. The base of the case must be cost. Nemertes has developed and validated an SD-WAN cost model that enables enterprise users to build that business case. The short version? SD-WAN deployments can cut millions from large WAN service bills. But connectivity is not the only avenue by which SD-WAN can drive savings; by providing cheaper and more transparent and automatic failover when WAN links fail, SD-WAN can reduce branch WAN outages and troubleshooting costs by 90%.

For IT and networking professionals the message is clear: now is the time to take a close look at your WAN architecture, with the aim of identifying locations that could benefit from higher bandwidth, lower rates, increased reliability, or all three. Model the cost of sticking with the current architecture and compare that against at least two SD-WAN solutions. If the SD-WAN numbers show significant potential savings over time, build a business case based on them, as well as other operational savings and any business value assigned by the business lines to faster branch turn-up.

The Issue

In the classic engineer’s formulation, “You can have it cheaper, faster, or better…pick two.” From time to time new technology comes along and, by changing the basic assumptions underlying existing solutions, manages to be cheaper and faster and better all at once.

SD-WAN promises to hit the trifecta. By changing the underlying assumptions about how you connect a branch to the WAN (and, indeed, what constitutes a branch) it offers the chance of improving agility (i.e. being faster) and performance and reliability (i.e. being better) while also reducing costs.

Building a business case for deploying SD-WAN invokes all three benefits but rests mostly on the strength of savings, whether in the form of expected cost increases avoided, or as actual cost decreases.

What is SD-WAN?

Let’s start first with definitions. Software-Defined WAN, or SD-WAN, incorporates several key concepts:

What is SD-WAN

  • Abstraction of edge connectivity: Making all the connections into a location useful as a single pool of capacity available to all services.
  • Virtualization of the WAN: Overlaying one or more logical WANs on the pool of connectivity, with behaviour and topology for each overlay WAN defined to suit the needs of specific types of network services, locations, or users.
  • Policy-driven, centralized  management: Key to an SD-WAN is the ability to define behaviors for an overlay WAN and have them implemented across the entire infrastructure without requiring device-by-device configuration.
  • Flexible traffic management for performance and security: SD-WANs can optimize traffic in many ways; foremost, they can selectively route traffic across links based on criteria such as link performance.

Types of SD-WAN

There are two key ways to provide these services in a WAN. Nemertes calls these overlay and in-net SD-WAN.

Overlay SD-WAN

In an overlay SD-WAN, the new SD-WAN appliances are deployed on an existing routed network, either behind the routers or replacing them as the branch connection to the WAN. SD-WAN appliances can also collapse the typical branch stack by replacing other branch WAN appliances such as optimizers and firewalls.

More than a dozen companies sell SD-WAN appliances, both physical and virtual (which allow extension of the SD-WAN into public cloud spaces such as Amazon EC2 or Google Compute Engine). Some are intended to replace routers, some to ride behind them, others can fill either role, and enterprise IT staff need to carefully evaluate each against their specific needs. For example, those with an aging router plant but mostly MPLS and Carrier Ethernet or broadband links may find router replacement very attractive. Those with a lot of older T1 or T3 connections that can’t or won’t be replaced with Ethernet may want to keep their existing routers in place, to terminate the older connectivity, while using the SD-WAN solution to supplement it with wired or 3G/4G broadband.

To read full download the whitepaper:
The CIOs Guide to SD-WAN


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