Understanding SDN Configuration: Software-Defined Networking

A software defined network (SDN) is a type of networking architecture that decouples the control plane from the data forwarding plane. Software-based controllers are responsible for directing traffic through your network to its destination.

SDN can be implemented in several ways, typically using APIs that surface rules configured in a centralized location. One example of this is, a zero-config VPN that provides software-defined networking for your devices, even when individual nodes reside in different physical networks.

What is SDN?

Traditionally, network routing has relied on dedicated hardware like routers and switches.

Software-Defined Networking (SDN) revolutionizes this by transferring these functions to software, effectively decoupling network control logic from the physical devices that implement it.

By layering software controllers over your existing hardware, SDN allows you to dynamically define network behavior through customizable rules and policies.

This approach enhances network flexibility, enabling on-demand configuration changes without the need for new hardware or alterations to existing devices.

Traditional Networking vs. SDN

• Traditional routing relies on dedicated hardware like routers and switches.
• SDN shifts routing functions to software, decoupling network control logic from physical devices.

Flexibility with SDN

• SDN uses software controllers to dynamically define network behavior through rules and policies.
• Network configurations can be adjusted on demand without requiring new or modified hardware.

Centralized Management for Administrators

• Administrators can oversee the network using a centralized interface.
• Tasks like setting up new routes, managing bandwidth, and monitoring health are simplified.
• No need to interact directly with individual hardware components; changes are applied automatically across the infrastructure.

Common SDN Use Cases

Here are some of the more common use cases we're seeing as SDN adoption is growing. Network functions virtualization (NFV) is also crucial in conjunction with SDN, as it enhances network flexibility and efficiency by decoupling network functions from hardware, enabling agile service delivery and centralized management.

Centralized network control

SDN should always be a contender when you need centralized control of a network and its components. A software-based approach lets you make changes to your architecture selectively, enabling dynamic allocation and management of network resources without having to interact with the underlying hardware. You can dynamically adjust your network to support new applications and devices as they come online.

Abstracting network functions

SDN abstracts network operation from its configuration. Applications that are connected using SDN components sit separately from the low-level technologies and infrastructure resources that create the physical network. This can make it easier to swap out specific pieces in the future without compromising the network configuration.

Additionally, virtual network functions operate independently from the physical infrastructure, contributing to enhanced adaptability and efficient management, especially in environments utilizing virtual machines.

Distributed networking

SDN supports distributed networking tasks such as edge computing, the Internet of Things (IoT), and remote user access. The centralized control plane means new devices can be onboarded without compromising reliability, security, or ease of management. is an example of a secure SDN model that fulfills this use case.

Data Center Networking

In the realm of data center networking, SDN proves to be particularly advantageous. By decoupling the control plane from the data plane, SDN enhances network performance, scalability, and reliability. This separation allows network administrators to manage and control the network more efficiently, reducing the complexity and costs associated with traditional networking.

One of the key benefits of SDN in data centers is the ability to create virtual networks. These virtual networks can segment different types of traffic, improving security and reducing the risk of network congestion. By isolating traffic types, virtual networks ensure that critical applications receive the necessary bandwidth and resources, enhancing overall network performance. Additionally, the centralized control provided by SDN simplifies the management of these virtual networks, allowing for rapid deployment and reconfiguration as needed.

Why Software-Defined Networking (SDN) Matters: Benefits

SDNs matter because they provide organizations with agility and flexibility by centralizing, changing, and monitoring routing decisions without compromising network performance or efficiency.

In addition to agility and flexibility, other benefits include:

• Separation of Logic and Data Transfer. SDN separates the logic of routing decisions from the physical action of transferring data, ensuring streamlined infrastructure operations.
• Dynamic Adjustments with Standardized APIs. Administrators can easily adjust network parameters in response to changing traffic demands. Standardized APIs simplify communication between components, making implementation and operations more efficient.
• Real-Time Adaptability. SDN adapts in real time to evolving traffic requirements, making it ideal for cutting-edge technologies. It’s particularly effective for distributed devices in IoT networks and environments relying on LTE and 5G, ensuring rapid data transfers and resilience to network changes.

Challenges of Implementing Software-Defined Networking (SDN)

The newness of SDN makes it a challenge to implement because it is difficult to find established examples to guide your deployment, and hiring staff with expertise can also be difficult.

In addition to resource and reference challenges, other drawbacks include:

• Learning New Management Tools. Transitioning to SDN requires learning new tools for configuring and monitoring your network. Network administrators accustomed to traditional networking methods will likely face a learning curve.
• Security Concerns. Moving routing functions to software introduces a new attack vector. A compromised SDN controller could expose your network's architecture and disrupt device configurations. This is why restricting access to SDN systems is crucial for minimizing risk.
• Potential Failure Points. The SDN controller is a critical component and its failure can lead to network-wide connectivity issues. This is why it's important to research the reliability of your SDN solution before deployment. Have teams develop and rehearse response plans for addressing unresponsive or malfunctioning controllers.

SDN Architecture Layers and Their Functions

SDN architecture comprises three main components: the application, the SDN controller, and the physical network devices that ultimately route packets. Here we explore the function of each layer:

Application Layer

The application layer contains network applications and services that use the SDN network.

• Key functions:
  • Communicates new routing requests.
  • Monitors broader network metrics, such as available capacity.
  • Acts as the interface for administrators to apply new configurations and manage network services.

SDN applications might also monitor broader information about the network, such as its available capacity.

Control Layer

The control layer houses the SDN controller, the brain of the network.

• Key functions:
  • Receives routing requests from the application layer.
  • Determines packet destinations using predefined rules.

SDN controllers use the available rules to decide each data packet’s destination. Although this layer determines how to route traffic, it doesn’t move any data through the network.

Infrastructure Layer

The infrastructure layer is comprised of the physical network devices and infrastructure, such as router and switches.

• Key functions:
  • Communicating with the SDN controller to execute routing requests.
  • Ensuring data packets are forwarded according to controller decisions.

Networking devices

The physical networking devices in your infrastructure communicate with your SDN controllers to action new routing requests. The device honors the decision made by the SDN controller and causes the data packet to be forwarded along the correct network pathway. The device could incorporate some protections to ensure it's sending traffic to an accessible destination.

How Data Flows Through the SDN Architecture

Data moves between applications, controllers, and physical devices using well-defined APIs. The two different layers are sometimes referred to using “northbound” and “southbound” terminology. This describes how dynamic rule changes made by administrators are communicated first to the network controller and then to the physical routers and switches.

Northbound APIs sit between applications and controllers. They allow applications to inform the network of new requirements, such as bandwidth requests and new routing rules. The controllers will relay information back to the application to confirm changes have been applied and report any errors.

Southbound APIs form the mesh between controllers and hardware. They let controllers influence the operation of physical devices to enact changes requested by the northbound APIs. Southbound APIs can be open source or proprietary solutions offered by individual hardware vendors.

Get started with SDN for Free

To give SDN architecture a try, get started with Tailscale for free by installing the client on each of the devices you want to access in your network.