SDN Deep Dive Series – Part 1 of 3: Architecture, Components, and Core Concepts

May 2013 · Estimated reading time: 15 minutes

In this first post of our three-part deep dive into Software-Defined Networking (SDN), we explore the architecture, key components, and the underlying principles that make SDN a transformative force in modern networking. SDN is not just a buzzword — it represents a radical rethinking of how networks are designed, operated, and managed. As of 2013, it is already influencing product roadmaps and enterprise strategies.

What Is SDN, Really?

At its core, SDN separates the control plane from the data plane. This decoupling allows centralized software (the SDN controller) to make decisions about where traffic should go, while the underlying devices (switches, routers, firewalls) simply forward packets according to those decisions. This architecture enables greater agility, faster deployment, simplified troubleshooting, and stronger alignment with business applications.

Why SDN Matters Now

In 2013, networks are under increasing pressure from cloud computing, mobile devices, virtualization, and big data. Traditional networks struggle with manual configuration, rigidity, and inconsistent policy enforcement. SDN addresses these challenges by making networks programmable, abstracted, and centrally managed.

Core Architectural Components

• SDN Applications: These express the intent or policy that should be enforced in the network — such as load balancing, access control, or routing optimizations.
• SDN Controller: The brain of the architecture. It receives requests from applications and translates them into instructions for the infrastructure.
• Network Infrastructure (Data Plane): The physical and virtual switches and routers that forward packets based on the controller's guidance.

Control Plane vs. Data Plane

Traditionally, the control plane and data plane are housed within each device — every switch and router maintains its own forwarding decisions. SDN breaks this pattern. The control logic is extracted and centralized, which simplifies policy enforcement and increases network agility.

Southbound and Northbound APIs

Communication in SDN is mediated by APIs:

• Southbound APIs: These connect the controller to the forwarding devices. OpenFlow is the leading standard here in 2013.
• Northbound APIs: These enable SDN applications to program the controller. Though not yet standardized, RESTful APIs are becoming common.

OpenFlow: The Leading Protocol

OpenFlow allows the controller to interact directly with the forwarding plane of switches and routers. It enables dynamic traffic management and offers fine-grained control over packet flows. In 2013, vendors like HP, NEC, Brocade, and Big Switch are shipping OpenFlow-compatible hardware.

Illustrative Architecture

Virtualization and SDN

Server virtualization has become ubiquitous in data centers. SDN extends this flexibility to the network layer. Solutions like VMware NSX and Open vSwitch (OVS) illustrate how SDN supports network abstraction in virtualized environments. This is key for VM mobility, multi-tenancy, and dynamic service chaining.

SDN Controllers

Controllers vary in design. Some are distributed (e.g., ONOS, Floodlight), others centralized (NOX, Beacon). Key capabilities include topology discovery, flow management, path computation, and failover. Most are open-source and programmable via Java, Python, or REST APIs.

Application Scenarios

• Data Center Automation: Automate network provisioning alongside virtual machine spin-up.
• Policy Enforcement: Apply consistent access controls across dynamic environments.
• WAN Optimization: Steer traffic based on application type or performance requirements.

Security Implications

Centralizing control logic introduces new attack surfaces. If the controller is compromised, so is the network. Design strategies must include redundancy, TLS encryption, access controls, and monitoring of API interactions. Defense in depth is non-negotiable in SDN environments.

Challenges in 2013

• Controller Performance: Can one controller manage large-scale traffic in real-time?
• Hybrid Deployments: Mixing SDN and traditional networks raises operational complexities.
• Northbound API Standardization: Lack of uniformity hinders application portability.

Industry Ecosystem and Progress

The Open Networking Foundation (ONF) has accelerated momentum around SDN standards, particularly OpenFlow. Meanwhile, Cisco’s ONE and Juniper’s Contrail demonstrate vendor-specific SDN architectures. The community is growing fast — startups, open-source initiatives, and traditional vendors are investing heavily.

Design Considerations and Future Proofing

Architects evaluating SDN should weigh:

• Controller placement and redundancy strategies
• Interoperability with legacy protocols (e.g., BGP, STP)
• Tooling for orchestration and monitoring (e.g., Puppet, Chef)
• Scalability of southbound connections (10K+ flows/sec)

Conclusion: Foundational But Evolving

SDN introduces fundamental changes in how we think about networking. This post covered the architectural pillars and operational motivations. In Part 2, we explore real-world deployments, controller platforms, and the growing vendor ecosystem surrounding SDN.

Eduardo Wnorowski is a network infrastructure consultant and Director.
With over 18 years of experience in IT and consulting, he designs high-performance network environments that align with business agility, security, and scalability goals.
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