Hybrid WAN Underlay: The Foundation for SD-WAN Success

One of the key messages heard consistently from SD-WAN vendors, irrespective of whether theirs is a platform built on proprietary appliances, or one leveraging “white-box” technology is that SD-WAN enables the widespread use of Internet in the WAN; replacing MPLS and driving network running costs down.

This is absolutely true; in the right circumstances, low-cost Internet can make really cost-effective enterprise network connectivity. After all, an xDSL circuit can be as little as 1/5th of the cost of an MPLS or Ethernet circuit of “equivalent” bandwidth. But is it reliable enough for widespread use across a multi-national enterprise WAN?

GCX has almost 20 years of experience working with broadband Internet and we can categorically state that over a period of time, Internet is less reliable than other connectivity types. In fact we see network faults occurring up to 4 or 5 times more on broadband Internet circuits than on more recognizable “enterprise grade” connectivity like Ethernet or MPLS.

Which begs the question; just how extensively can the Internet be used in an enterprise network?

To answer this we should put the debate around SD-WAN to one side for a moment and return to some basic principles; applying “fit-for-purpose” technologies and techniques to known requirements and variables.

On the one hand, Internet is typically cheaper than MPLS. But MPLS is more robust and less prone to faults. The Internet is based on the principle of net-neutrality, offering “best-efforts” performance only. Conversely MPLS offers differentiated performance through Quality of Service and comes backed by end-to-end performance guarantees.

Most multi-national enterprises have a range of locations of different types spread all over the world. Each location has a set of “needs” to which network technology should be matched. Some locations may have large user-bases who access time-sensitive applications hosted in off-premises data centers or the Cloud. Others may be manned by small numbers of users who mostly use non-time-sensitive applications – maybe even SaaS.

There is simply no single “right” answer. In practice, most multi-nationals will continue to benefit from the use of a mixture of technologies which will likely include Internet and MPLS; often at the same site with an Internet circuit acting as a low cost (but dormant) back-up.

On the whole. using the Internet end-to-end is unlikely to be an effective wholesale replacement for MPLS. Performance fluctuations attributable to everything from contention ratios to “circuit-flapping”, and sub-par performance from poor network peering, can make “latency-sensitive” applications unworkable over long distances over the Internet.

But all is not lost. Why not take advantage of low-cost Internet as the “last mile” (replacing the costly traditional local loop with high bandwidth, “business” broadband), and connect this into a software-defined “intelligent” core network to create a true Hybrid WAN underlay? This way you take traffic off the Internet before peering and poor performance can kill the user experience.

Connecting a smart SD-WAN device to broadband Internet transport, which in turn connects securely to an intelligent core network, offers the optimum blend of cost and application-specific performance for most large, widespread enterprise networks.

And this is certainly a viable solution.

But as more and more traffic is destined for the Cloud (for example accessing servers running Cloud-hosted apps in a public Cloud environment), it is critical that traffic takes an optimum path to these services. This may be by local “breakout” with traffic going over the Internet end-to-end, or it may be over the “performance” connectivity if the Network Provider offers direct Cloud Connectivity like GCX does with CLOUD X Fusion. Within an SD-WAN environment, these routing decisions are made at an application level and can change in real-time as network conditions change … but only if you have the right connectivity options available in the first place.

And since SD-WAN technology almost unanimously supports link-bonding, more bandwidth can easily be added as bandwidth demands grow. Only now, the SD-WAN uses performance parameters as the means for routing traffic, rather than destination-based routing protocols used by MPLS today.

This all sounds pretty simple, right?

In reality there’s any number of “gotchas” and traps to avoid if you’re going to harness the potential of the Internet in the enterprise Hybrid WAN.

As an illustration, GCX systematically takes  the following into account on every Hybrid WAN deployment:

ISP choice; Product choice (bandwidth, residential vs. business, cover hours, unlimited vs. metered usage); Commercials (cost, contract length); Infrastructure separacy and local loop unbundling; Circuit procurement; Circuit hand-off (RJ11, Ethernet, modem, DSL splitter – on this point note that not all options are supported by all SD-WAN hardware); Static vs. fixed IP addressing; Timeliness and correctness of circuit delivery; Burn-in periods and attenuation; Bandwidth profiling and training; Circuit stability and flapping; Customer service procedures and fault-management; Change and upgrade options; Performance reporting; Chronic fault management, circuit replacement and “black-listing”; SLAs; Billing….

And since SD-WAN technology almost unanimously supports link-bonding, more bandwidth can easily be added as bandwidth demands grow. Only now, the SD-WAN uses performance parameters as the means for routing traffic, rather than destination-based routing protocols used by MPLS today.

And there’s more where that came from.

Problems can arise quickly if you choose a product not suited for use in an enterprise WAN, or if service levels and cover hours fall short of your requirements. In these cases, no matter how loud you shout, you may struggle to get a problem resolved quickly. While this is not ideal when your users can’t access their critical Cloud applications, or when you have to resort to manual credit card transactions on a busy Saturday afternoon, it is mostly avoidable.

The key to success is knowing what you are doing; choosing the right connectivity option in the first place, and then operating it successfully in partnership with the Internet Service Providers (ISP). And while this sounds manageable for 1, 2, 3 … maybe up to a dozen connections, how scalable is it for most enterprises as the numbers grow?

If SD-WAN is the future, what about the underlay? Well with the right choices and expectations mixed in with a dollop of know-how and a dash of creativity, the Hybrid WAN underlay really is the recipe for SD-WAN success.


CLOUD X WAN is the complete global managed SD-WAN solution with hybrid WAN underlay connectivity for any site, anywhere.
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