What Exactly is SDN?

Quick Definition: Software-defined networking (SDN) is a networking approach that separates network control from the underlying hardware infrastructure. SDN separates the control plane from the data plane, allowing network administrators to manage and control networks in centrally based software controllers. 

Software-defined networking is a godsend for those classically trained among us or prospective new techs looking to improve their skill set. 

But what exactly is SDN, and why should you care? Today, we'll cover that and a bit more. 

What is Software-Defined Networking?

Software-defined Networking (SDN) is an architectural approach in networking in which the control plane is decoupled from the data plane. This centralizes the control and programmability of network behavior through software-based controllers. SDN enables greater agility, flexibility, and efficiency when managing and configuring networks.

At the heart of each SDN is a software management system. This application controller manages the entire software-defined network, which makes an SDN so powerful. In this video, CBT Nuggets trainer Jeff Kish provides a high-level look at SDN.

In the classic world of network management, network administrators needed to craft careful note-taking systems. The health of the organization depended on those notes, and network admins were required to manually configure and administer each network component.

That model allowed for a lot of mistakes and failure. There's a reason network engineers are paid so much money. Then, software-defined networks entered the scene. 

Software-defined networks are primarily software-driven. So, the software control center handles the configuration process instead of having network engineers manage each network component by hand, such as routers, switches, and firewalls. 

SDNs leverage APIs to integrate with DevOps tools like Chef, Puppet, or Terraform, enabling network engineers to automate network provisioning and configuration. This integration helps engineers use version control software and automation applications for efficient network deployments, enhancing agility and scalability in network management.

Understanding SDNs Layers

SDNs consist of three layers: the application layer, the control layer, and the infrastructure layer. Each layer plays a crucial role in the network's function and management.

Application Layer 

The application layer represents the top layer of the architecture where network applications and services reside. These applications use the programmable interfaces provided by the SDN controller to implement functions such as traffic management, security enforcement, quality of service (QoS) policies, and network optimization. 

The application layer's flexibility enables network administrators to deploy custom-built or third-party applications tailored to specific networking needs. Whether fine-tuning traffic policies, implementing robust security protocols, or optimizing network resources, the application layer is a playground for shaping the network's functionality.

Control Layer 

At the heart of SDN architecture is the control layer, which houses the SDN controller, often dubbed as the network's 'brain.' This layer manages network behavior, orchestrates communication with the underlying infrastructure, and facilitates tasks like policy enforcement and routing decisions.

The SDN controller functions as a central command center, implementing real-time oversight and control over network operations. The controller oversees traffic steering, policy enforcement, routing decisions, and resource allocation.

The control layer also fosters seamless communication between the SDN controller and the underlying network infrastructure, ensuring coordination and synchronization of network-wide operations. The control layer empowers administrators to manage complex network environments easily.

Infrastructure Layer 

The infrastructure layer operates at the lowest level of the SDN hierarchy. It includes physical network devices such as switches, routers, and other hardware components. The layer transmits data packets, ensuring seamless connectivity and efficient data transfer between network endpoints.

The infrastructure layer works closely with the control layer, following the directives and instructions issued by the SDN controller. This symbiotic relationship creates dynamic adaptation and responsiveness, enabling the network to quickly adapt to changing conditions and requirements.

What are the Benefits of Using an SDN? 

Now that we understand SDNs let's talk about why so many folks are excited about them. There are a variety of benefits to using an SDN, including: 

• Centralized Management: SDN allows centralized management of the entire network through a single controller, enabling administrators to easily configure, monitor, and troubleshoot network devices from a central location.

• Improved Agility: With SDN, network configurations and policies can be dynamically adjusted through software, allowing you to rapidly deploy new services, applications, and network changes to meet evolving business needs.

• Better Scalability: SDN simplifies network scaling by separating network control from the underlying hardware. This makes it easier to add new devices, nodes, or services with minimal manual configuration.

• Increased Flexibility: SDN enables network administrators to define and enforce network policies and traffic management rules through software, providing greater flexibility in controlling network behavior based on application requirements, user needs, or security concerns.

• Optimized Traffic Flows: By centralizing network intelligence, SDN facilitates more efficient traffic engineering and optimization. It allows for dynamic rerouting of traffic paths, load balancing, and prioritization of critical applications or services.

• Enhanced Security: SDN enables the implementation of granular security policies and access controls across the network, allowing for the quick detection and response to security threats or anomalies through automated enforcement mechanisms.

• Lower Operational Costs: SDN simplifies network management tasks and reduces manual configuration, leading to lower operational costs. 

What is the Difference Between an SDN and a Regular Network?  

In a classic network architecture, network admins explicitly created routes, VLANs, and firewall entries. Otherwise, network engineers configured both the devices' intent and actions to make them function properly. 

Network admins interact with the control software in a software-defined network instead of individually interacting with each component. Instead of defining rules and actions, network engineers only need to define intent. The management software then determines the rules and actions to make that intent actionable. 

For instance, if a network admin wants to block all network traffic from a specific app, they would define access controls for that app in the network management software. The management software then contacts the firewall to configure the appropriate heuristic rules, etc. This all occurs in Layer 3 of the network. 

What if you need to connect multiple business locations to the same network? The management software can do that automatically, too. It will create the WAN infrastructure and orchestrate the processes required to bring the entire business network under the same fabric despite its distance from the central network core. 

Can You Use Any Network Equipment in an SDN?

Do you want to deploy a software-defined network? Easy enough! Pick out your preferred vendor solution and go to town. Most network equipment vendors have a variety of predefined product packages that fit the bill. 

That wasn't the original idea of an SDN, however. The software-defined network was initially meant to be universal. The goal was to be able to use products from Cisco, Ubiquiti, or Palo Alto together. The reality is that the dream hasn’t come true yet. 

Vendors like Cisco are working hard to make their equipment more cross-compatible with other vendors. Many vendor solutions are already cross-compatible with newer orchestration software. Still, for the best results, you'll want to use vendor hardware verified to work with your organization's requirements. 

Learn More About SDN Technology

SDNs make network management, security, and efficiency far easier than a traditional network. Nonetheless, this article is only the Kool-aid to excite you about managing an SDN. To learn more, check out this CCNP: Automation and Orchestration course.

If you are a beginner with the concept of an SDN, consider enrolling in an online training course that explains network orchestration concepts. CBT Nuggets also offers training for network orchestration solutions based on those concepts.