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Shrinking the Stack with the New SDN: Automate, centralize control, and shed some unsightly pounds of network gear

Author: John Burke, CIO & Principal Research Analyst

Software Defined Networking (SDN), with a shift to focusing on programmability and the virtualization of networks, network functions, and appliances, is shaking up all kinds of networks. Interest in SDN is driven by two desires: the desire to exert end-to-end control of network behavior from a central control point via changes in policies rather than node-by-node reconfiguration, and the desire to reduce the cost and complexity of the network.

By separating the control plane of the network (where decisions are made about how to handle traffic) from the data plane (which implements those decisions), SDN makes it possible for network applications to implement both performance and security policies on any network port, physical or virtual, data center, WAN, or branch. By giving central policy immediate enforcement, SDN eliminates the latency between policy changes and policy implementation that plagues most networks. SDN also allows easy overlay of virtual networks on physical ones, in the same way server virtualization let multiple virtual servers share a single physical host, promoting security through segmentation. And it presents APIs that allow for automation to create, manage, modify, and remove networks reliably and at scale without massive increases in staffing.

It does all this, typically, on hardware lacking custom silicon (a “whitebox” switch) and able to host any of several switch operating systems, able to be controlled by any of several network operating systems/SDN controllers. Or without switch hardware at all, running entirely in virtual computing space.

Network applications replace network appliances, shaping network behavior via the controller. Replacing specialized hardware with virtual machines running on commodity hardware, and breaking monolithic multifunction appliances into swarms of collaborating Virtualized Network Functions (VNFs), further eliminates the dependence on specialized network hardware. In the data center, this can mean using commodity server hardware in place of specialized network appliances. Likewise in branch wiring closets, where virtualized WAN appliances or VNFs can share a generic server. Replacing “the stack” in each closet with a single, flexible host can drive down the capital expense of a new branch, as well as the time it takes to light one up. It can also ease upgrades, de-provisioning, and additions to that stack operationally.

IT leaders should:

  • Begin testing SDN systems now: deploy a system based on centralized, policydriven management of diverse data-plane devices, and learn how to write effective policies and how to use APIs to automate activity.
  • Understand and make plans to root out proprietary protocols in your networks.
  • Explore whitebox switching as your data plane.
  • Look for opportunities to collapse network appliance stacks.
  • Build use cases: look inside the data center first, for ways automated provisioning and management can speed operating processes; look also for specialized use cases, such as dedicated monitoring networks; and look to SD-WAN.

Table of Contents
  • Executive Summary
  • SDN Doesn’t Mean What It Used To
  • Key Principles in SDN
    • Control-Plane Separation
    • Centralized Management
    • Virtualization
      • Virtualizing Appliances
      • Virtualizing Functions
      • Virtualizing Networks
    • Disaggregation
      • Whitebox World
  • Braving the Brave New World
  • Conclusion


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