Does SD-WAN have the potential to kill off MPLS?

With a proven ability of connecting Enterprise networks over large, geographically-dispersed locations – including branch offices and datacentres – Software-Defined WAN is one of the hot topics being discussed across IT departments at the moment.

29 November 2017

With the promise to reduce costs and complexity of Enterprise WANs by automation, you can clearly see why SD-WAN is causing a stir. But does it live up to the hype?

I was recently asked if I thought SD-WAN had the ability to truly replace traditional MPLS technology. With all the marketing information in the public domain, I answered with conviction – yes, it most certainly does. However, since then I have been looking into the SD-WAN offerings in more detail, delving into Quality of Service (QoS)…and changing my opinion. MPLS is here to stay. First, we have to understand the concept that SD-WAN is an “edge” technology, which in essence means the intelligence lies on the perimeter of the network. So how is QoS deployed? It’s done by measuring parameters including packet loss, jitter and latency at the edge of the network, using this information in conjunction with dynamic path control and Forward Error Correction (FEC) on multiple internet-facing links. After this, SD-WAN then has the ability to elect the best path among the paths available. 

However, in a scenario where all paths are congested, SD-WAN doesn’t have the ability to protect business-critical traffic. This is a significant disadvantage to traditional MPLS where full QoS can be applied to a link and prioritise traffic, allowing protection on key applications for the Enterprise.

Also, as an edge technology, SD-WAN will not be aware of how to route traffic externally, and thus sees the WAN as “fluffy Cloud”. This can potentially lead to inefficient routing whereby cheap internet links may result in an array of latency issues. But the intrinsic nature of MPLS technology as a private network with the user has full control over traffic engineering, ensuring that these issues can be readily mitigated.

The benefits of SD-WAN are hard to deny, from cost to agility/flexibility to ease of use/deployment to increased security...but MPLS technology is here to stay. Enterprises may reduce their dependence on the MPLS; however, in its current form SD-WAN won’t kill it off. My advice is to research carefully and take advice to ensure the product can technically deliver the right performance characteristics required.

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