SDN Performance – A Red Herring

Terry Slattery
Principal Architect

I keep hearing about how SDN will fail because of high round-trip latency from an switch or router platform to the controller. This is much like the criticism I heard about TCP performance in the mid-1980s. My first TCP throughput performance test using TTCP between a VAX 780 running BSD Unix and a Sun workstation showed 30KB/s (yes, Kilobytes per second!) It was only after Van Jacobson started researching TCP performance that we started to see improvements in throughput. Today, TCP is able to scale from dialup to long, fat pipes.

The same types of performance improvements are possible with SDN systems. A good example is the research on controller performance ( The primary change was to implement multi-threading and I/O batching. The improvements were quite significant: a 33-fold improvement in response time. The authors note that the improvements were just the simple ones that could be quickly and easily implemented. The point is that there is a lot of room for significant improvements in SDN controller performance.

Distributing the SDN controller function across multiple hardware platforms will help make sure that controllers are near the switches in order to minimize the request/reply latency. Intelligent location of controllers in the network is something that we’re going to have to learn. I’m sure that there will be one or two important performance-related rules of thumb that will be developed as we gain more experience with SDN network design.

Critics are correctly pointing out a weakness in SDN. However, we will learn how to overcome this weaknesses, at least to the extent that it allows us to take advantage of the benefits that SDN provides. We just need to instrument the system so that we can collect the data necessary for us to understand the limitations and learn how to work around the problems that we find.


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Nick Kelly

Cybersecurity Engineer, Cisco

Nick has over 20 years of experience in Security Operations and Security Sales. He is an avid student of cybersecurity and regularly engages with the Infosec community at events like BSides, RVASec, Derbycon and more. The son of an FBI forensics director, Nick holds a B.S. in Criminal Justice and is one of Cisco’s Fire Jumper Elite members. When he’s not working, he writes cyberpunk and punches aliens on his Playstation.


Virgilio “BONG” dela Cruz Jr.

CCDP, CCNA V, CCNP, Cisco IPS Express Security for AM/EE
Field Solutions Architect, Tech Data

Virgilio “Bong” has sixteen years of professional experience in IT industry from academe, technical and customer support, pre-sales, post sales, project management, training and enablement. He has worked in Cisco Technical Assistance Center (TAC) as a member of the WAN and LAN Switching team. Bong now works for Tech Data as the Field Solutions Architect with a focus on Cisco Security and holds a few Cisco certifications including Fire Jumper Elite.


John Cavanaugh

CCIE #1066, CCDE #20070002, CCAr
Chief Technology Officer, Practice Lead Security Services, NetCraftsmen

John is our CTO and the practice lead for a talented team of consultants focused on designing and delivering scalable and secure infrastructure solutions to customers across multiple industry verticals and technologies. Previously he has held several positions including Executive Director/Chief Architect for Global Network Services at JPMorgan Chase. In that capacity, he led a team managing network architecture and services.  Prior to his role at JPMorgan Chase, John was a Distinguished Engineer at Cisco working across a number of verticals including Higher Education, Finance, Retail, Government, and Health Care.

He is an expert in working with groups to identify business needs, and align technology strategies to enable business strategies, building in agility and scalability to allow for future changes. John is experienced in the architecture and design of highly available, secure, network infrastructure and data centers, and has worked on projects worldwide. He has worked in both the business and regulatory environments for the design and deployment of complex IT infrastructures.