A Complete Guide to Software-Defined Networking

You cannot escape the pervasiveness of software.

Mobile, cloud computing, big data, social networks, virtualization, and the Internet of Things (IoT) have all contributed to software becoming a critical economic enabler of practically every business on the planet. And these technologies are still evolving.

Software is eating the world and networking is no different.

Traditional software that runs on conventional hardware is spectacularly bad at providing a satisfying consumer experience. Most business networks are controlled by people and administered with management tools in a reactive and manual process. But this is changing thanks to the improvements in automation and programmability achieved by software-defined networking (SDN).

Software-defined networking holds substantial promise for radically changing how networks are built and operated by reducing cost, improving performance, and increasing functionality. With the advent of SDN solutions, such as software-defined wide area network (SD-WAN) software, the expectations for automation and programmability in network control software and hardware have risen dramatically.

That means instead of using physical cables to connect different components of a network, SDN creates virtual communication channels that IT teams can reconfigure quickly with software. The phrase "software-defined" in networking means that specific configurations are no longer hard-coded into the hardware devices of the network infrastructure, but can be managed through software or alternate interfaces.

Software-defined networking is a subset of the broader concept of software-defined everything. Proponents see it as the next generation of software-based dynamic network control. Software-defined networks eliminate the need for IT staff to visit each location to configure networking devices physically. The result is a highly flexible network that can adapt to changing traffic patterns.

As businesses continue to adopt cloud and mobile solutions, the expectations for rapid provisioning and automation accelerate beyond what existing networks can provide. The response is an SDN architecture that reduces capital expenditures while simplifying network operations. As with many IT trends, SDNs are transforming networks within companies and between enterprises and service providers globally.

What makes SDN technology so compelling is that it gives engineers new ways to program their networks, making it possible for them to create network configurations that previously would have been impossible or prohibitively expensive.

Why do businesses need software-defined networking?

Organizational network traffic patterns have shifted considerably in recent years as more systems have been transferred to the cloud and demand for applications to be mobile-friendly has grown. Although conventional network topologies made sense when applications ran on a basic client-server basis, something more flexible is now essential.

It's no secret that applications in the data center have become deeply dependent on predictable network performance and can quickly respond to service changes through self-service mechanisms. This has led to a more software-centric view of the network, with many application teams seeking more control over their application delivery. In comparison, IT teams seek tighter control over infrastructure complexity and costs.

Today's businesses need technology that ensures their operations are always up and running, flexible, and scalable to support business growth. Software-defined networking delivers seamless network control, operational efficiency, and accelerated business results.

SDN enables business networks to be dynamically configured on demand and respond transparently to various service changes by integrating these functions into a single control plane. In short, network switches and routers become programmable, enabling IT teams to achieve absolute control over how their network resources are utilized. This ultimately allows them to deliver a higher quality experience for the end-users.

As a result, businesses can more effectively distribute network resources. Since the network is controlled by software, it’s more agile, simple to handle, and ready to adapt to new use cases. SDN enables the programmable nature of networks through software applications using open APIs.

Organizations can also use software-defined networks to improve network security by categorizing business traffic. Specific networks can be classified as highly secure and transport critical data, while others can be public. If a hacker gains access to a public-facing web server, they are limited to that portion of the network and cannot access other segments, such as the protected data center networks.

What is software-defined networking not about?

Software-defined networking is a revolutionary new approach to network management that enables businesses to easily control and program their systems. SDN can solve many problems, but before shifting to an SDN architecture, companies should clearly understand what software-defined networking isn't.

• Software-defined networking is not intent-based networking (IBN). Both intent-based networking and SDN can comprehend network configuration and interaction across numerous devices, but they are different. Although SDN separates management control from devices, it maintains a device-centric view of the network. The directives in IBN are abstracted at a higher level, moving them from device-centric to business-centric.
• Software-defined networking is not network automation. Even though SDN and network automation are both based on code, they are not the same. SDN only covers a subset of automation. Coupling network automation with virtualization enables businesses to introduce new technologies such as SDN into the infrastructure quickly.

Understanding how traditional networking works

Knowing how traditional infrastructure networks work is an essential part of understanding how SDN works. Traditional networks are characterized by end-to-end connectivity, meaning every computer can communicate directly with every other computer.

This allows computers to use various technologies, such as local area networks (LANs), wide area networks (WANs), urban wireless networks, and even satellites to connect to the same network.

Traditional network infrastructure is made up of hardware and software. It allows computation and communication between users, services, applications, and processes. Fixed-function network equipment, such as switches and routers, is the foundation of traditional networks. Each of these devices has a specific purpose that works well with the others and helps to maintain the network.

Networks are portrayed as one-dimensional with lines connecting nodes, but that’s not the case. A network has three dimensions known as "planes": the data plane, the control plane, and the management plane. A plane is an abstract representation of where certain operations take place in networking.

Data plane

Also known as the forwarding plane, the data plane is a network layer with infrastructure to carry network traffic. The data plane functionality in conventional networks is provided by firmware in switches or other devices. 

The data plane's actions are dependent on the control plane. The data plane traffic must be segregated and regulated to protect the router and network from various attacks. These risks can originate from both valid and malicious traffic, and the data plane security strategy must account for all scenarios.

Control plane

The control plane is the network layer that carries signaling traffic and is responsible for routing. A control plane performs its task independently. It contains network protocols for communication between network elements, such as routing, signaling, link-state protocols, and additional control protocols for building network services.

Management plane

The management plane is a subset of the control plane that handles device management and administrative traffic. Securing the management plane is equally important as securing the control plane for effective router and network functioning. Unauthorized access invariably results from a compromised management plane, allowing an attacker to further compromise the IP traffic planes by adding routes and changing traffic flows.

Switching and routing in computer networks are traditionally done using hardware components with the above three planes. Recently, the trend has been shifting to software-based network devices running on general-purpose central processing units (CPUs).

How does software-defined networking work?

Software-defined networking is becoming increasingly popular in big data centers, WANs, branch offices, campuses, data center networks, and telecom networks for an exciting reason: it increases network efficiency. With its ability to dynamically allocate resources to reduce maintenance costs and operational complexity, SDN is emerging as a powerful tool for modern networks.

In software-defined networking, the software is decoupled from the hardware. The control plane, which determines where traffic should be sent, is moved to software by SDN. But the data plane, which sends information, remains in hardware. This allows network administrators who utilize SDN to program and administer the whole network from a single control point rather than by device.

SDN eliminates the need for individually managing devices, such as traditional routers or switches. This has implications for the architecture, economics, and security of an enterprise network.

While there’s no one model for software-defined networking, the topology of this kind of network has changed over time. The OpenFlow paradigm, which was crucial in SDN's early development and standardization, was one of the earliest SDN communication protocols.

This strategy, managed by the Open Networking Foundation (ONF), requires businesses to deploy physical network elements, such as SDN controllers, routers, and switches, explicitly designed to support the OpenFlow protocol. As SDN grew, many people discovered that the basic paradigm was too restrictive and devised alternative methods.

As a result, network virtualization models emerged, allowing virtual networks to be created. These virtual networks can be separated from the underlying network hardware and controlled by software.

SDN architecture

Software-defined networking comprises three major components that may or may not be physically placed together: the application layer, the control layer, and the infrastructure layer.

Application layer

The application layer contains the standard network applications or functions businesses utilize to enhance application speed, simplify IT, and boost security. Examples of these systems are intrusion detection systems, WAN optimization controllers (WOCs), load balancing systems, and application firewalls.

Traditional networks require dedicated network equipment for these duties. A software-defined network substitutes the device with an application that manages data plane behavior through a controller. Programs on the application layer transmit particular network instructions to the SDN controller.

Control layer

The control layer is in charge of a network's policies and traffic flow. The requirements presented by the application layer are processed by the control layer, which subsequently sends them to the underlying network infrastructure. The control layer also sends data from the infrastructure layer back to the application layer to improve functionality.

The SDN controller, which links the application and infrastructure layers, is part of the control layer. SDN controller software offers a centralized view and control over the whole network. Network teams use the controller to regulate how the underlying infrastructure's forwarding layer handles traffic.

The controller is also responsible for enforcing regulations that govern network activity. Network administrators set policies that are implemented consistently across all nodes in the network. Network policies are rules that define what degree of access to the network traffic has, how many resources it is permitted, and what priority it is given.

Infrastructure layer

In the data center, the infrastructure layer houses the network's actual switches and routers. These network devices are in charge of crucial forwarding functions and data processing capabilities and gather critical information,such as network use and topology, to report back to the control layer.

The above three layers communicate using northbound and southbound APIs. The northbound API allows communications between the control and application layers, while the southbound API will enable communications between the control and infrastructure layers.

Northbound APIs

Applications in a software-defined network rely on the controller to inform them of the network infrastructure's availability to determine what resources are available. The SDN controller can automatically guarantee that application traffic is routed according to the set policies. The apps communicate with the control layer via northbound APIs, informing them of their required resources and their intended destination.

The control layer orchestrates how available resources are allocated to the apps in the network. It also employs intelligence to determine the best path for the application in terms of latency and security. Northbound APIs are typically RESTful APIs. Orchestration is fully automated and does not require manual configuration.

Southbound APIs

The SDN controller uses southbound APIs to connect with network infrastructures such as routers and switches. The network infrastructure is informed of the path the application data must take, as determined by the controller.

The controller can modify how the routers and switches move data in real time. The data no longer depends on devices and routing tables to determine where it travels. Instead, the controller's intelligence makes informed judgments that improve the data's route.

Types of software-defined networking

Next-generation applications require new network architectures to handle more traffic, provide better performance, and reduce cost. Software-defined networks lead this effort by shifting networking control from traditional hardware to software running on commodity server hardware.

However, several SDN architectures exist that vary in their implementation details, controller structure, and management interfaces.

• Open SDN: An open SDN architecture controls the virtual and physical devices that route data packets using open protocols.
• API SDN: This topology controls data flow to and from each device by utilizing programming interfaces, also known as southbound APIs.
• Overlay model SDN: SDN builds a virtual network on top of the current hardware, offering tunnels with channels to data centers. The model then assigns devices to each channel and distributes bandwidth in each channel.
• Hybrid model SDN: This topology blends the best features of SDN with traditional networking, allowing the best protocol for each kind of traffic to be allocated. The hybrid SDN is frequently utilized as a phase-in approach to SDN.

Software-defined networking vs. network function virtualization

The networking sector is always on the cutting edge of change, dealing with a constantly altering economic and technological landscape while simultaneously managing increasingly high consumer expectations. Some of the most visible disruptors have been the increased prevalence of smartphones and internet-based apps, the 5G boom, shifting WAN needs, and the creation of novel traffic patterns from IoT connections.

When paired with a rapid increase in demand for dynamic bandwidth and on-demand services, flattened revenues, and a pressing need to decrease costs, service providers and businesses have no choice but to change their networks and operations.

Software-defined networking and network function virtualization (NFV) are two concepts gaining a lot of traction. The terms are often used interchangeably within the industry, even though they achieve different goals.

Software-defined networking

Software-defined networking is a networking architecture that enables dynamic and programmatically efficient network configuration to increase overall network performance, making networks more agile and adaptable. SDN controls networks by decoupling the control and forwarding planes to enable more automated provisioning and policy-based network resource management.

SDN serves its users with a method to control network services through software that makes networks centrally programmable and allows for speedier configuration. It enables companies and service providers to adapt rapidly to changing business demands and requirements, eventually improving network control.

Network function virtualization

Network function virtualization is a network architecture that lets network operators deliver services faster and for less cost by shifting features like firewalls and encryption from dedicated hardware to virtual servers. This consolidates different functions into a single physical server and lowers total costs. NFV enables multiple network operators to implement network policies without worrying about where functions should be placed in the network or how to route traffic.

NFV is a method of virtualizing network services (such routers, firewalls, and load balancers) and enabling them to run on virtual machines. Multiple operating systems can share a single hardware processor with the help of a hypervisor called a virtual machine manager. Compared to networks created with traditional networking equipment, NFV provides high-performance networks with better scalability, flexibility, and adaptability at lower prices.

The telecom industry initially developed NFV to address the increasingly complex process of managing and provisioning network services. There’s also a growing demand for new business models and innovative service offerings. The use cases for NFV are increasing and evolving, from virtualized mobile core networks and carrier Ethernet services to retail and enterprise WAN and IoT networks.

SDN vs. SD-WAN

The fast-paced nature of business and changes in technology have resulted in an increased need for responsive networks. Modern companies need agile, reliable, and secure networking solutions to operate efficiently. The increase in mobile usage, cloud adoption, and the advent of IoT has added further complexity to traditional networks.

To meet this challenge and deliver the benefits of software-defined networking, businesses use a software-defined wide-area network (SD-WAN) that provides secure and reliable access across an entire enterprise network.

However, with SDN being one of the most talked-about technologies today, organizations are also focused on understanding what SDN is all about and how it can help enterprises build more responsive networks. 

SDN and SD-WAN are two related ideas that describe networks that can be controlled and monitored using software. They both represent essential technology shifts that will impact how businesses and technology providers move and manage network traffic in the future. Understanding their differences is critical in creating agile networks.

Software-defined networking

Software-defined networking was created to satisfy computing demands in both LANs and service provider networks. The objective was to create dynamic, flexible, and scalable connections within the data center and on core networks to accommodate changing needs.

SDNs are directly programmable, allowing for a flexible, centrally managed platform that separates the control plane, which decides where traffic should be routed, from the data plane, which defines how traffic should be delivered.

Software-defined wide area network

Software-defined wide area network is an extension of SDN that focuses on the network edge (the area where a device or local network interfaces with the Internet) and enables companies to connect several distant sites by utilizing the internet and multiprotocol label switching (MPLS). It includes a set of utilities geared at the edge, such as firewall capabilities.

The major difference between the two is that SD-WAN provides a wide-area network that connects many locations, making it an SDN in the WAN. Another significant distinction is that SD-WAN is managed by the vendor rather than by internal resources. SD-WAN requires less effort from a network engineer because the vendor provides the service.

SDN use cases

SDN adoption has created a buzz in IT circles. Quantifying its impact remains a challenge because it has many applications across the enterprise. There are three broad categories where organizations are using SDN: networks, storage, and workloads.

To get a sense of where SDN is headed, let's look at some of the typical use cases being implemented across the industry.

• Scaling business data center: Enterprises have utilized SDN to create scalable data centers, which means engineers can use more or less resources to efficiently manage software-defined data storage and consumption.
• Application deployment: SDN allows application teams to release and control applications from a central hub network.
• Securing IoT architecture: Although IoT devices provide convenience and options, they also provide hackers and other data thieves several access points. With SDN, IoT developers can offer a central, customized protective layer that helps to safeguard the process.
• Support intent-based networking: With intent-based networking, teams can instruct the network what it needs to perform in accordance with the specific business objectives. An SDN-enabled infrastructure can customize the functioning of various components in a way that harmonizes with large-scale goals.

Challenges of SDN

Software-defined networking has ushered in another network revolution like open-source software, public cloud computing, and virtualization. It’s changed the way networks are built and managed in the enterprise. SDN has provided enormous flexibility, driven multi-fold gains in efficiency, and expanded the scope of automation to include software-defined network operations, network security, and SD-WAN services.

No matter how you plan to use SDN, it’s imperative that you understand the challenges of SDN and how it will affect your organization to undue risk.

• Security risks: While SDN makes networking easier, it also poses a security risk. Centralized administration is a single point of failure so if it fails, the entire network suffers.
• Northbound API standards: Vendors and open source entities are creating different APIs for their SDN controllers since there’s no widely acknowledged standard for northbound APIs. This complicates application development since developers must create numerous versions of apps in order for them to work with different controllers.
• SDN controller bottlenecks: When an SDN controller has just one instance, it might create a bottleneck for a network with a lot of traffic, routers, and switches. There's basically too much to connect with for a single controller instance.

Benefits of SDN

Businesses that invest in SDN are often attracted to its capacity to handle data-intensive applications. Beyond that goal, SDN offers a plethora of advantages that make it a worthwhile endeavor. Listed below are a few of the most significant perks.

• Increased adaptability: SDN helps companies be more agile by separating the control plane, which is responsible for routing network traffic, from the data plane, which sends data through routers. The high-bandwidth, dynamic nature of today's applications need this scalability.
• Improved use of network resources: Organizations that switch to SDN can save money on operating expenses (OPEX) by using virtual resources.
• Increased programmability: SDN helps IT teams easily install, protect, and optimize network resources since there are no vendor-specific protocols or proprietary software. The network is directly programmable because the control plane is separated from the forwarding plane.
• Simplified management: A software-defined network results in an overall easier-to-operate architecture because it does not require highly skilled network specialists to operate it.

The new way of networking

As a steadily evolving industry, networking is always looking for emerging technologies to suit customer demands. Switching to SDN is an essential milestone for businesses. It provides excellent efficiency improvement in managing network resources, enhances resiliency, and simplifies service deployment.

Enterprise networks are evolving from device-centric to intent-based. Learn how intent-based networking (IBN) can help you build networks that are intelligent and agile.