Sep 19, 2016
We have been discussing Software-Defined WANs (SD-WANs) for about eighteen months. As is the case with any new approach to networking, the initial focus of that discussion was on basic topics such as what is meant by the phrase SD-WAN. As we get closer to the time when a lot of companies will start to deploy SD-WANs the focus of the discussion has begun to shift to questions such as: What is the value of adopting an SD-WAN?
Most of the discussion of the value of an SD-WAN to date has focused on the potential of an SD-WAN to either reduce the amount of money that a company is currently paying for WAN circuits, or to reduce how much that cost goes up over time. In addition, some SD-WAN solutions enable network organizations to eliminate routers and the associated costs. Router elimination can be done either coincident with the initial deployment of the SD-WAN solution or at some future time. Given that most companies can get approval to deploy a new solution if they can show that that solution reduces cost, these kinds of cost savings will continue to be a major part of the discussion of the value of an SD-WAN.
There are, however, other benefits that accrue from the deployment of an SD-WAN including:
In an SD-WAN, network functions such as security and QoS can be coordinated at a policy level, with the controller handling all of the details needed to implement those policies across multiple WAN links. Many SD-WAN solutions also support sophisticated fingerprinting to identify applications and sub-applications. This enables the solution to choose the appropriate end-to-end path to meet the security or QoS requirements.
Most discussions of SD-WANs use examples in which there are two links out of each branch office. While that approach does improve security and application performance, it may not deliver application performance which is both consistent and predictable through a wide range of network conditions, including brownouts and outages. To achieve that goal, additional links may be required and, wherever possible, those links should be diversely routed. It is also necessary that the SD-WAN solution can utilize all available bandwidth at all times.
One of the primary advantages of a software-defined network is that it reduces the amount of effort that is associated with tasks such as configuration and provisioning. It does this by centralizing control and allowing network organizations to configure and provision hundreds of devices as if they were one device.
In a traditional WAN there is a single data path from origin to destination. If that path becomes unavailable, there is an outage until a new path is established. A key feature of an SD-WAN controller is its ability to support multiple active paths from the origin to destination. In normal operating conditions, this capability of SD-WAN increases both the performance and scalability of the solution. In the case of an outage, this capability increases availability because there will still be at least one active path from origin to destination.
One way that an SD-WAN increases the agility of the IT organizations comes from the decoupling of the virtual networks from the physical networks, as well as being able to guarantee complete isolation of each user of the SD-WAN. One advantage of this isolation is that is enables an IT organization to allow application developers to run their applications in a production environment without impacting production traffic. This is particularly important for an IT organization that either already has, or soon will embrace DevOps. Another advantage of decoupling the virtual networks from the physical networks is that the virtual networks enable virtual machines (VMs) to be dynamically moved between physical servers with no manual intervention.
There is no doubt that cost savings will be a key component of the business case that many organizations create to justify adopting an SD-WAN. However, in many other cases benefits such as:
will, as a minimum be a part of that business case, and in some cases will be the dominant component of that business case.
It is important, however, to note that the currently available SD-WAN products and services are just the first generation of such services. We can expect that over the next several years that successive generations of SD-WAN products and services will be brought to market. These new products and services will provide functionality not found in the current products and services and they will likely target use cases in addition to branch office connectivity. As a result, the business case for those products and services will likely include benefits beyond what was discussed in this blog.