It seems that we in the networking industry have been talking about evolving the WAN for well over 20 years now. The traditional \u201chub and spoke\u201d WAN that we\u2019ve all grown accustomed to was ideally suited for client\/server computing, where users were in branches and applications were located in the data center.Over the years there have been small, incremental changes to the WAN that have improved the performance and security of the network. MPLS is now the de facto standard instead of frame-relay and WAN optimization has become a core service for many organizations. These changes did indeed improve the WAN marginally, but it\u2019s time to overhaul and re-architect the WAN.RELATED: SDN start-up targets enterprise WAN complexityMost companies have survived with a legacy WAN for years, so why do I now think WAN evolution is a business imperative? The primary reason is that compute is shifting from client\/server and the internet to cloud and mobile. Cloud and mobile computing create entirely different traffic patterns than legacy computing models. Also, business agility is a top priority for company leaders, and that drives the need for IT agility and, more specifically, network agility. As a result, today\u2019s networks are highly inflexible.Also, all these changes we\u2019ve made to the network over the years have increased the complexity of the WAN to the point where making even small changes requires an enormous amount of work. Between security, visibility tools, routing and optimization technologies, network managers need to worry about multiple protocols, service chains, QoS and a bunch of other factors. That\u2019s why WAN evolution is needed today and that shift is to a software-defined enterprise WAN.Think of the software-defined enterprise WAN (SDE WAN) as the equivalent of an SDN in a data center. A SDE WAN has the following attributes:Abstraction of network functions. Legacy networks connected locations to one another. This was sufficient as all the corporate resources were in branch offices or a data center. An SDE WAN connects workers to applications or content, which is critical today as workers can be anywhere, and so can apps and data. Ideally, the abstraction of the network would be driven by business policies, as that\u2019s what\u2019s really driving change in corporate IT today. This becomes more important as businesses shift to a hybrid cloud model and resources are moved on and off the company network.Hybrid networks. As I mentioned above, MPLS is the dominant WAN protocol today and businesses back up the MPLS connection with internet VPNs or even LTE connections. However, networks currently use an \u201cactive \u2013 passive\u201d architecture where the backup connection only becomes active when the primary fails. With SDE WAN, all connections would be active and traffic could be isolated over any network connection via automated path selection. Companies that move to this model should take a serious look at minimizing spend on MPLS and being more aggressive with Internet and\/or LTE connections. Path selection and secure traffic isolation can give security and performance characteristics that are on par with, or even better than, MPLS.Network Functions Virtualization (NFV). Part of the challenge of managing a WAN today is managing multiple appliances required to deliver WAN functions. These need to be delivered as virtual functions on a single device. Also, the virtualized network services should be centrally managed and have the capability of being deployed "on demand."One solution provider that\u2019s focused on delivering the SDE WAN is CloudGenix, who came out of stealth mode this morning. Santa Clara-based CloudGenix uses a combination of a \u201clean\u201d branch office appliance and centralized controllers to deliver customers a scalable, secure SDE WAN. The company uses SDN principals to virtualize hybrid networks, secure the network and assign business and IT policies to create a simpler, easier-to-manage WAN with a significantly reduced branch office\/device footprint. Last month, I wrote about how the WAN could be a beneficial starting point for SDN deployments, and that is the primary focus of CloudGenix.The explosion of different types of applications, hybrid clouds, mobility, and network complexity is driving the need for WAN evolution, and \u201cgood enough\u201d is no longer good enough. An SDE WAN is a simpler WAN that\u2019s easier to manage, more agile, and better aligned with today\u2019s computing trends.