Data Centers

Software-defined WAN solves a big data problem

Internet circuits have traditionally been considered too unreliable to replace dedicated circuits. Software-defined WAN vendors hope to change that perception.

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Traditional network design dictates that a consistent, dedicated connection should perform better than a faster, unpredictable internet connection. I discovered this isn't so cut-and-dried.

A few years ago, I led a team that built out an 85-site video conferencing solution. One of the insights we uncovered was that the video conference experience was best on faster internet VPN connections vs. slower dedicated MPLS connections. At least internet VPN outperformed MPLS most of the time — it proved extremely difficult to shape traffic via policy for optimal circuit provisioning and usage. Software-defined wide area network (SD WAN) solutions enable the capability of leveraging the right mix of expensive and inexpensive WAN links.

A big data problem

Using policy-based routing to shape traffic across disparate WAN link types is a big data problem. The desired network policy is to route application traffic over the best available connection. The complexity comes into view when you define the applications with connection attributes, and the connectivity performance isn't constant.

Backup traffic may be suitable for network internet connection; conversely, voice and video traffic should be best suited for a dedicated connection. However, when the destination side of the dedicated connection experiences jitter or delay, it would be ideal to route voice and video over the internet connection during this period.

To make these decisions, the network infrastructure must collect and analyze a tremendous amount of flow data. You can use network tools to model averages, but the information isn't helpful when making real-time decisions.

It's also a challenge to manually apply policies across a large infrastructure. This is the challenge I ran into in the video conferencing solution build out. The Comcast internet connection in Philadelphia would outperform the AT&T MPLS connection to California, but the MPLS connection would outperform the internet connection to Chicago. Multiply this challenge by 85 sites, and you have a big data problem.

Enter SD WAN

SD WAN is the separation of the control plane from the data plan, which means network devices continue to forward IP packets while a controller makes policy decisions on how those packets forward. The controller is normally an x86 server that has the capability to collect metadata from end points. The end points sit in front of WAN connections and create an overlay. Based on the application and network state, the controller dictates the flow of traffic through the network overlay.

Because the network controller is an x86 device or a cluster of x86 devices, the analysis capacity is more than any existing network protocol running on dedicated network devices. The controller can analyze traffic and determine optimal network paths for individual applications as well as individual flows. SD WAN solutions enable a greater level of circuit flexibility; an organization can leverage several inexpensive broadband circuits and reduce the reliance on dedicated connectivity.

For example, a large site could leverage an aggregate of a 1Gbps Google Fiber connection, a 1Gbps Verizon FIOS connection, and a 45Mbps MPLS connection. The network manager may find after a year of use the 45Mbps MPLS connection has a utilization rate of only 5%. The network manager could leverage this information to negotiate lower pricing or reduce the speed of the MPLS circuit. Either way, the organization saves money on the next telecom contract.


There are many variables when considering a SD WAN solution, starting with the cost of the solution vs. your telecommunication outlay. Depending on the size of your WAN, there may not be enough cost savings to justify SD WAN. It's also important to remember that circuit optimization is just one consideration — SD WAN solutions also offer security, WAN monitoring, and improved application performance through policy-based traffic shaping.

Do you believe SD WAN can solve some of your WAN networking pains? Post your thoughts in the comments.

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About Keith Townsend

Keith Townsend is a technology management consultant with more than 15 years of related experience designing, implementing, and managing data center technologies. His areas of expertise include virtualization, networking, and storage solutions for Fo...

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