ONF Certified SDN Associate (OCSA) – Part 2

The OCSA exam tests your understanding of components in an SDN framework, your ability to articulate the fundamental workings of networking and the OpenFlow protocol, as well as your knowledge of vendors, solutions and projects available in the SDN landscape.


This is the second part in a series of posts that review the blueprint for the OCSA exam and provide descriptions and resources to help you achieve the certification. The posts are broken down by the sections detailed in the OCSA blueprint.

Part 1

Domain 2: SDN Concepts – 25%

From the Blueprint:

Describe the fundamental characteristics of SDN, definitions, use cases, and history.

  • History of SDN (Clean Slate, Ethane, OpenFlow┬«, donation to ONF)
  • What is SDN? (control and forwarding)
  • SDN Value Proposition
  • SDN Use Cases
  • SDN Use Cases in the Data Center
  • SDN Use Cases in Campus Networks
  • SDN Use Cases in Service Providers
  • SDN Use Cases in the Enterprise
  • SDN Use Cases in Mobile Networks
  • The six characteristics of an SDN Network
  • SDN Devices (Controllers, Switches, Orchestration, API’s)
  • Overlay Networking Abstractions (NFV, VxLAN, etc.)

History of SDN

Clean Slate is the R&D program at Standford started focused on evolving technologies. Some program members included Rob Sherwood of Big Switch networks, Nick McKeown of Barefoot Networks, the founders of Forward Networks, and famously, Martin Casado, whom was the leading force behind Ethane.

Ethane was the Ph.D. work of Martin Casado and the team at Stanford, which later became OpenFlow, starting the disruption SDN has brought to the networking industry. His company Nicira was purchased by VMware for mountains of money and is the foundation of NSX.

What is SDN?

The OCSA being an SDN certificate – you should know how to answer. The funny thing is, it’s a running joke in the industry what SDN actually means. Even Martin Casado jokes that he’s not sure what SDN is anymore.

What’s important to know here is the ONF definition of SDN.

The physical separation of the network control plane from the forwarding plane, and where a control plane controls several devices.


SDN Value Proposition

Here’s a quick rundown of some SDN value propositions:


Let’s face it, the rest of the Infrastructure teams and Application Developers are tired of waiting on the Networking teams to provision access needs, with the business suffering as a result. The speed to spin up network services should match that of spinning up compute resources. This agility is one of the goals of SDN.

Reduced Risk

Policy-based networks are the way to go, with everything enforced per-user, per-application, per-VM, and so on. This not only speeds up the process, but it reduces the risk of something being misconfigured or out of compliance.

Operational Efficiency

The network can operate more efficiently with the separation of control and data planes.

Reduced Spend

This is still up for debate, but the consensus mostly has been a predicted savings in CAPX and OPEX when moving to SDN. I can see a potential for OPEX savings relating to network virtualization and the automated services targeted to operate it.

SDN Use Cases

SDx Central put together a nice page of use cases worth checking out. I’ll list out some brief examples you should know for each topic.


SDN Use Cases in the Data Center

  • Big Data Optimization
  • Mice/Elephant Flow Optimization

SDN Use Cases in Campus Networks

  • Campus NAC
  • Seamless Mobility & BYOD
  • Video Streaming/Collaboration
  • Management Simplification

SDN Use Cases in Service Providers

  • Optical Network Optimization

SDN Use Cases in the Enterprise

  • Unified Communications Optimization
  • Security

SDN Use Cases in Mobile Networks

  • Mobile Network Virtualization

The six characteristics of an SDN Network

  • Plane Separation
  • Simplified Forwarding Element
  • Centralized Control
  • Network Automation
  • Virtualization
  • Openness

SDN Devices (Controllers, Switches, Orchestration, API’s)

Nice and straightforward illustration from http://www.zeetta.com/sdn/


Overlay Networking Abstractions (NFV, VxLAN, etc.)

Here on overlaid.net, we love overlays. However, for brevity, I’m not going to speak to detail about this in this post. What you should know is what overlays are, not necessarily the nitty-gritty details.

For example, an overlay could be as simple as an IPSec or GRE tunnel between two points across the Internet. Within a data center, an overlay could be VXLANs, used to extend layer 2 networks over a layer 3 network for scalability, automation, and multi-tenancy.


Continue on to Part 3 of this series which covers Domain 3 of the blueprint.

David Varnum


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1 Response

  1. REJE VAS says:

    Very nice and useful blog for OCSA Aspirants. It would be good if you can also provide a few sample /model questions that would help us to take a self evaluation.

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