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Do wide area networks need to get software-defined?

Should you upgrade your wide area network to SD-WAN? Learn what factors you should consider before making the leap.

SD-WAN aims to make wide area networks simpler and less expensive to design, build and operate -- to offer simplified,...

application-centric, centralized management of a complex pool of WAN links.

To decide whether SD-WAN is right for their network, IT staff need to consider several factors:

  • hard and soft costs associated with managing their network
  • the need for and degree of resilience
  • the need for and ability for the wide area network to deliver excellent performance for all apps
  • whether they want to hand management over to a service provider

Hard costs …

Hard costs come down, typically, to router and MPLS costs; these need to be compared to SD-WAN appliance and broadband costs. Device costs can be significantly lower in the SD-WAN space, when compared to multifunction branch routers, or can be about the same as router costs.  It is only when the SD-WAN device (or managed service) is replacing multiple devices -- say, a router and a WAN optimizer -- that you can be fairly certain of hardware cost reductions. Connectivity costs, on the other hand, can come down by 80% to 90% on a per-Mbps basis when IT swaps broadband Internet links for some or all MPLS links in a given location. In fact, costs can come down that steeply even when IT puts in massive increases in bandwidth and redundant broadband links. Most business cases for making an SD-WAN shift rest on the reduction in connectivity costs.

… and soft costs

Soft costs center on engineer hours needed to manage the various use cases of the wide area network and maintain the WAN at a given level of performance. By abstracting away many of the details of routing traffic intelligently across multiple links (and multiple types of links) to meet service and performance targets, SD-WAN can greatly ease management of the wide area network. 

Likewise, SD-WAN can reduce the amount of emergency work needed to deal with link failures or transient link performance issues by automating the rerouting of traffic and rebalancing and reprioritizing across the remaining links. This reduces or eliminates down time from the user perspective as well, another source of soft-dollar costs. Soft-dollar savings can be as high as hard-dollar savings, or higher when downtime has been a significant problem. However, soft-dollar savings can be a more difficult sale than hard-dollar savings -- though it is important to document what soft savings can be expected, it is usually not enough to build a business case.

WAN resilience, performance

As noted, SD-WAN can make having multiple links into any site both affordable and easy to manage, thus making WAN resilience a reality for many sites that could not previously afford it (and much more affordable for those who already have it). As businesses find it less and less acceptable to have downtime anywhere for anyone, resilient connectivity is increasingly important even for small and remote facilities.

In choosing a product, IT staff should be looking at a variety of factors:

  • The way in which it aggregates capacity: Is all the bandwidth available to any application?
  • The way in which it manages traffic across links: Can it split traffic for one application across multiple paths for better throughput? Assure packet delivery with multipathing or error correction?
  • Its flexibility in controlling performance and adding security. How many factors can it use in defining a policy for network traffic, beyond protocol and port information. Factors to consider include application function (e.g., printing vs. data input); user; location of endpoints of traffic stream; time of day, week, month and year; cost associated with different link types.
  • Form factor and position in the network: Does it replace the router -- or does it sit in front of, behind, or next to the existing router? Is it a physical appliance (and if yes, is it custom silicon or x86 base?). Or is it a virtual appliance, and if so, is it running on-site -- and if so, where? Or it is in cloud?
  • What about WAN topologies supported? Is it always a mesh, a hub and spoke, can it assign a topology per policy based on application-specific needs?

And, of course, IT should be looking at a shift to SD-WAN as another point at which to ask: do they still want to manage the WAN at all, or is this a good time to look for a managed SD-WAN provider instead?

Bottom line: Do you need SD-WAN?

SD-WAN is appealing, both because it abstracts away and automates some of the most complex aspects of making use of mixed, redundant network connections. In addition, that abstraction makes it easier and more effective than ever to incorporate broadband Internet links into the WAN. This all greatly reduces WAN costs.

But how to know if you really need SD-WAN? You can answer that question by answering these. An organization should seriously consider SD-WAN

  • if it is spending a lot more time and money on providing connectivity than it can afford, on an ongoing basis.
  • if it is not getting the resilience it wants everywhere it wants.
  • if it is having trouble getting good performance on demanding applications.
  • if it is having trouble getting the WAN to serve the needs of divergent applications -- not just with respect to performance, but also with respect to security and compliance.

If yes is your answer to most or all of these questions, then now is a good time to look at SD-WAN products and tools.

Next Steps

Case study: Learn what happened when these clinics switched to SD-WAN.

Who’s trying SD-WAN next year? Survey says…

How exactly does SD-WAN save money?

This was last published in October 2015

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