Addressing hybrid network challenges with SD-WAN

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SD-WAN overlays could transform how hybrid WANs are designed and operated. What should the enterprise consider?

In previous articles I outlined one of the most clear-cut use cases for Software Defined WAN: replacing traditional Internet-based VPNs with a centrally-managed SD-WAN solution. This is easy for enterprises to relate to, and the benefits of deploying this type of project can be considerable.

However, many enterprises deal with a much more complex hybrid WAN, and the challenges with this type of environment can be substantial. A hybrid WAN means that multiple technologies are integrated to deliver the end-to-end solution; this can include MPLS, VPLS, point-to-point circuits and Internet VPNs. Traffic flows between end users and applications can span multiple technologies and multiple boundaries of management responsibility. I've worked with many global enterprises that operate networks like this, and I hear several recurring complaints:

  1. There is a lot of wasted bandwidth, as backup Internet circuits are often left sitting idle in case of a failure on the MPLS network.
  2. Performance for Internet applications is often poor, as traffic is back-hauled over a slower MPLS link to reach a data center Internet breakout point.
  3. Application-level reporting is difficult, as the network often consists of in-house and vendor-managed components, each with their own systems and tools.

Is SD-WAN a solution?

As SD-WAN offerings continue to mature, several vendors are extending the capabilities of their products to address hybrid network topologies. There are some similarities to the approaches that are emerging:

  • Overlays become the new network foundation. Overlays are a feature in most SD-WAN offerings, and the concept becomes essential to understand in hybrid networks. Overlays typically consist of tunnels established between the SD-WAN endpoints, defining the paths over which traffic can flow. Locations connected by multiple transport types (e.g., MPLS and Internet VPN) will have multiple overlay tunnels, allowing the SD-WAN solution to send traffic along a specific path.
  • Bandwidth becomes a commodity, with telemetry. Since packet forwarding decisions are moved to the overlay (with underlying circuit-level routing masked in most cases), the bandwidth in the network is available as a pool of capacity for the solution to use. However, one key characteristic of advanced SD-WAN solutions is the level of telemetry data that is collected to influence forwarding decisions - not just at the circuit level but along an entire path. The SD-WAN solution "knows" not just that a 2Mbps MPLS circuit and 10Mbps Internet broadband circuit is available, but the characteristics of each path they are part of: end-to-end latency, packet loss, jitter, throughput bottlenecks, etc. Making packet forwarding decisions on this range of metrics is hugely difficult to achieve in traditional networks.
  • Coexistence with legacy protocols is important. As SD-WAN is adopted in more complex enterprise environments, the need to understand (and participate in) traditional routing protocols becomes essential. This includes the use of eBGP on MPLS networks and a potential long list of protocols in the LAN, including BGP, EIGRP, and OSPF. SD-WAN vendors are rapidly adding these capabilities to their offerings, but enterprises adopting the technology today will need to use workarounds or simplifications in some cases to work with the current state of the technology.

A fast-moving space

Many of the hybrid networking capabilities of SD-WAN vendors are still in their early stages. It's easy to see why the vendors are addressing this space, as complex hybrid enterprise networks represent a huge opportunity for change. Interest in SD-WAN overall continues to grow at a rapid pace; the release of Gartner's Market Guide for SD-WAN (in December 2015) shows that its enterprise clients are looking for specific details on the capabilities of this technology.

One of the key questions that enterprises will need to consider is who manages the environment, particularly as SD-WAN starts to be used in more complex networks. This is what Gartner said in its December report:

At this stage of market development, the key target market is the enterprise that manages its WAN in-house, because SD-WAN solutions can significantly reduce the operational burden of deploying and managing WAN solutions. However, to improve the lead times and flexibility of their managed WAN services, some network service providers are beginning to take advantage of SD-WAN technologies.

It remains to be seen whether major service providers will be effective in delivering agile, flexible solutions like SD-WAN to their overall customer base, or whether only a subset of clients will be able to benefit from this technology. I'll continue to look at delivery and management models for SD-WAN in a subsequent article. 

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