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Software-Defined Networking (SDN): Definition, Layers, and How Does it Work?

SDN or "Software Defined Networking", is a new concept in networking that appeared back in 2008, revolutionizing the way we connect, control, and provision resources. Traditional networking is hardware-based, making use of routers and switches to control network traffic. However, the use of these networks had a number of drawbacks. In particular, manual configurations were time-consuming and costly and led to weak network security and poor scalability.

Comparatively, SDN is a newer, more refined form of networking that is "software-based" as opposed to traditional hardware-based networking. Software-Defined Networking employs software-based controllers or APIs to direct underlying hardware infrastructure and network traffic flow.

Initially, SDN can be traced back to the separation of the control plane and data place used in the public switched telephone network in order to simplify management and control. This architecture was soon adopted for use in data networks, and SDN was born. SDN doesn't necessarily exist to replace existing traditional networks, but to add value to what we already have. They are, instead, enhancing and sharpening legacy networks.

With SDN, regardless of the complexity of the underlying network technology or the type of devices used, operators can manage the entire network and all devices running on it consistently. The goal is to improve overall network control and enable enterprises to quickly adapt to changing business requirements.

Here we'll be taking a closer look into SDN networking topology, how it works, and why it is relevant today.

What is Software-Defined Networking (SDN)?

The world is digitizing at a rapid rate, and businesses are expected to keep up with on-demand and customizable services. One of the most important factors to consider is "data". Your modern networks need to be efficient enough to handle large amounts of data, and multiple types of data without slowing down.

This is where SDN comes in. SDN is a type of architecture that allows network managers to configure, control, manage, and secure network resources quickly and efficiently through a centralized control plane.

How exactly and why exactly was SDN formed?

In the beginning, only closed and proprietary networks existed. That was until students at Stanford's computer science department created the Ethane project, which used open-source software to split control planes and data planes in a network architecture. This design further led to the creation of the OpenFlow protocol.

The OpenFlow protocol is one of the first SDN components that kickstarted the networking software revolution. Simply put, the OpenFlow protocol allows network administrators to manage and direct traffic passing through routers and switches regardless of which vendor offers the underlying router or switch.

This further gave birth to SDN. The technology that separated the control plane from the underlying data plane in networks. SDN architectures offer intent- or policy-based management of the network as a whole. This resulted in a data center network that was better aligned with the needs of application workloads through quicker, fully-automated provisioning, management, and visibility.

Today, SDN is being used in security services, network intelligence, and monitoring, distributed application control, and cloud integration. Organizations use SDN to improve scalability, improve policy control and simplify network complexities.

How Does Software-Defined Networking (SDN) Work?

Let us better analyze "Software Defined Networking". Software-Defined Networking is a type of architecture that delivers a centralized, programmable network. It centralizes management by abstracting the control plane from the data plane across the network.

Let's simplify this a bit more.

The control plane, which determines where to send traffic, is shifted to software, whereas the data plane that actually forwards the traffic is left with hardware devices. The data plane will therefore handle the traffic based on the configurations supplied by the control plane which is now centrally managed, all thanks to SDN.

Now, the network administrator can use the SDN to program and control the entire network through one access point, which traditionally would have to be done manually through each device.

Let's take the example of a data packet that arrives at a network switch. The switch (which is a device on the data place) will get guidance from the control place as to where the data packet is to be forwarded. The centralized controller will send the packet handling rules to the switch and, in this way, traffic flow is controlled.

What are the Advantages of Software-Defined Networking (SDN)?

There are a number of advantages of Software Defined Networking:

  • Simplified Operations: Running a larger complex network can be incredibly time-consuming and manpower intensive. Software-Defined Networking simplifies such large, complex networks and allows administrators to easily monitor and administer the network from one central location. The administrator can further make changes to any network switch rules (that dictate how to deal with incoming data packets) accordingly. In this way, data packets can be allowed through; certain packets may be prioritized over others; and some data packets may be blocked entirely, as required.
  • Improved Visibility Across Networks: Network visibility implies how well an organization is aware of traffic flow on their networks, and the behavior of traffic on those networks. SDN allows administrators to get real-time visibility into their network traffic flow. We must also consider improvements in network management here as well. SDN allows for centralized management of the entirety of the network instead of operating multiple individual devices. This improves the ease of monitoring and allows administrators to quickly deploy security policies.
  • Reduced Hardware Footprint: Traditional networks demanded that you add new hardware and provision more resources if you wished to expand network capacity. Comparatively, Software Defined Networking allows you to expand networks without having to invest in additional physical hardware. This reduces the hardware footprint of organizations and also reduces overall costs.

What are the Disadvantages of Software-Defined Networking (SDN)?

Now, let us take a look at some of the disadvantages of software-defined networking.

  • Security Risks: On the one hand, SDN technology can improve security, but on the other hand, it can also lead to new security concerns. Recall, that the SDN controller is fully centralized. This means that if a hacker were to target the central controller, he could have access to the entire network. SDN networks, therefore, have a single point of failure.
  • Configuration: If you're hoping to implement an SDN-type architecture in your network, you will need to make changes to your entire network infrastructure. This complete reconfiguration of your network can be incredibly complex and will lead to increased costs.
  • Slow Adoption: SDN networks can be incredibly helpful, but not all business enterprises are quick to adapt to this change. Small enterprises with limited resources do not see the cost of SDN configuration and deployment as worth the benefits it has to offer.

How Does SDN Help With Security?

There are many ways Software Defined Networking can help strengthen network security. Let's talk about SDN centralized network control. In traditional networks, each device on the network decides locally how it will treat incoming traffic.

SDN, on the other hand, allows you to control the routing of all traffic across the network through a single centralized controller. It allows for visibility across the entire network topology and architecture.

This increased visibility and control means that you can selectively stop data packets from advancing further in the network by simply denying access. The best part is, that you can do so without disrupting the remainder of your network.

Traditionally, security patches would have to be manually configured for each device, but with SDN's centralized controller, each device can be updated remotely without having to physically access each device. This way, your network will always be updated against evolving network security threats.

What are the Architectural Layers of Software-Defined Networking (SDN)?

The SDN architecture consists of 3 distinct layers, i.e. the applications layer, the control layer, and the infrastructure layer. The control layer is typically sandwiched between the application layer and the underlying infrastructure layer. From here, these layers use southbound and northbound APIs, or application programming interfaces, to communicate between each layer.

  • Application Layer: The applications layer includes network programs and applications that communicate the desired network behavior and requirements to the underlying SDN control layer. In traditional networks, you would instead use a dedicated firewall as an appliance or a load balancer. But in SDN, we use an application layer to control and manage the data plane.
  • Control Layer: Next, we have the control layer, which connects the application layer and the infrastructure layer. This layer represents the centralized SDN controller software from which the administrator can take charge of the entire network, manage policies, and oversee traffic flow.
  • Infrastructure Layer: Finally, we have the infrastructure layer. This is the underlying network of physical switches and routers in the network. These devices forward network traffic towards their destinations based on the rules and policies provided by the controller.

What is the Importance of Software-Defined Networking (SDN)?

Over the last few years, networks have been receiving higher traffic demands as more and more enterprises and end customers rely on networks for sales, customer service, document sharing, and nearly all types of communication. SDN helps organizations meet these demands.

SDN allows for a centralized view of your entire network for more efficient management and automation of your network services. Hardware-bound networks were limited in their functions, scalability, and flexibility. SDN on the other hand improves this flexibility and allows for higher scalability.

What's more, this centralized controller will continue to offer the same level of control regardless of the underlying hardware you use. In this way, you can customize your network services and infrastructure to include hardware from multiple vendors as desired.

Is SDN Important for Data Security?

Yes, Software Defined Networking is considered important for data security. SDN may have its own networking challenges, but it is still a step ahead of legacy networks when it comes to security. With SDN, you can add on enhanced infrastructure backed up by the cloud and take advantage of the security benefits the cloud offers. In many cases, the cloud is far more secure than on-premises infrastructure.

Moreover, with SDN controllers, you can ensure that all security policies are being automatically applied across all underlying devices. SDN provides a "granular" approach to data security where you can filter out specific data packets without affecting the remainder of the network's operations.

Is SDN Important for Web Security?

SDN is known to improve cybersecurity and web security measures across your network. Growing business needs include interconnectivity between IT and OT networks. Cybersecurity is a critical aspect of how this interconnectivity can be achieved. SDN can be used to build a more secure interconnection.

For one, administrators can use policy implementations to manage the security state of the network. Security management policies describe how the network is treated in response to changing threat levels for a proactive, preplanned type of security control.

Software-Defined Networking also offers significant improvements in packet sniffing capabilities or packet analysis techniques that allow for the detection of intruder activity or malicious content. If we combine SDN packet sniffing with analytical tools that respond to the detection of malicious traffic, it stops the threat before it can move on to do any real damage.

Is SDN Useful for the Speed of Network Connection?

Yes, SDN has greatly improved data sending capabilities across networks. Traditional networks used devices, each instructed individually on how to direct traffic flow. The device would continue to follow these instructions until updated with new policies. However, to do so, you would have to reconfigure the switches, routers, and other devices across the network which could take weeks or months at times.

SDN on the other hand, allows us to reconfigure devices from one central location. This way, we can control packets traveling anywhere across the network, no matter where they started their journey. This increased visibility makes it a lot easier to direct and control data packets with efficiency and agility.

Is SDN Useful for Digital Transformation?

More and more organizations are focusing on digital transformation initiatives, and at the forefront of this development is software-defined networking (SDN). SDN allows organizations to continue to handle increasingly complex enterprise networks with agility and maximum control. Networks need to keep up with changes in capacity and usage, this is what SDN can help with.

SDN allows you to simplify network complexities to keep your organization more agile. It will further allow you to scale up and down according to your network needs, making it easier to reduce congestion through intelligent automation.

Instead of investing in physical hardware when you need to expand, you can deploy intelligent network solutions via the cloud on an as-need basis, paying only for that which you use.

On top of it all, SDN will also allow you to test out new processes without impacting the remainder of the network, making it easier to implement new solutions during your digital transformation. With centralized management comes more agile operations and execution, seamless automation, and efficient provisioning of network resources.

What are the Major SDN Service Providers?

Here are some of the leading SDN service providers operational today:

  • Cisco: Cisco SDN allows for the automation, provisioning, and management of networks through software interfaces. Today, Cisco is one of the leading providers of SDN technology. Cisco ACI or Application Centric Infrastructure, allows for application agility and data center automation, whereas Cisco DNA allows for AI and ML for network managers to monitor, troubleshoot, and optimize network control.
  • VMware/Nicira: VMware acquired Nicira's Network Virtualization Platform back in 2012 for $1.2bn. Their SDN, NSX, or Network Virtualization and Security Platform, allows for a software-defined approach to networking.

What are the Differences Between Cloud Computing and Software-Defined Networking (SDN)?

Cloud computing tends to differ from Software Defined Networking.

  • We can better understand the differences by looking at their functional goals. Cloud computing is meant to provide users with access to data and resources anytime, anywhere. SDN has slightly different goals; it allows a network administrator to manage, construct, and control network resources such as traffic and bandwidth from a centralized controller.
  • The cloud is made up of a set of servers that are accessed over the internet, allowing users easy access to these servers remotely for use. It is essentially used as a form of infrastructure and computing services. On the other hand, SDNs are a centralized approach to networking that provides more granular control over resources.
  • Cloud computing does not necessarily have to be in a centralized system, but SDNs nearly always provide a centralized controller for the user.

What are the Global Server Companies that Use SDN?

Here are some examples of the top global server companies that are using SDN today:

  • DELL: DELL, most commonly known for its computing technology and one of the top worldwide server companies, has long since embraced the concept of SDN. Their data center networking solutions provide customers with a choice of SDN implementations based on their unique requirements.
  • HPE: HPE or Hewlett Packard Enterprise, is another leading provider of computing technology and worldwide servers. Their server management software is popular for offering automation, simplicity, support, and security. Their SDN infrastructure technology is used to provide unified access to the software-defined network.
  • Huawei: Huawei is one of the world's leading telecommunications providers, but you may also know them through their smartphones. Huawei has been using SDN for years and is also committed to providing SDN network solutions to its customers.

What is the Future of SDN?

We've discussed how SDN was formed, how SDN works, and the advantages and consequent drawbacks of SDN. But what about the future implications of this technology holds?

There are plenty of ways in which SDN will remain equally relevant, or even more relevant, in the future.

Considering the evolution of 4G to 5G, 5G has not been fully exploited yet and SDN will play a pivotal role in its advancement. SDN in combination with 5G will offer lower latency and competitive pricing. 5G networks will further be used across all types of facilities and larger enterprises, in order to continue smooth operations in coordination and easily resolve problems that arise in the network.

In the future, we can expect SDN to become a technology that is more responsive, fully automated (so it works with minimum human intervention), and highly secure (solving the "single point of failure" issue). Estimates show that the global SDN market will grow up to $61 billion by the year 2023. This is not surprising as more and more companies continue to shift to digitized operations, each using SDN to facilitate this change.

Does AWS Use SDN (Software-Defined Network) Technology?

Yes, Amazon Web Services, or AWS, uses SDN. In fact, many call AWS the world's largest implementer of Software Defined Networking. Their global network is present at a massive scale, they are one of the leading global eCommerce providers after all. They utilize this in conjunction with their data centers and servers to offer a wide range of networking services.

Cloud providers such as Amazon further use SDN to efficiently build private, public, and hybrid clouds to increase the agility of network flow and application deployment. Google is another example of a mega cloud provider that uses SDN. These early adopters will lead the SDN movement toward dynamic and evolving applications in large-scale environments.

Is Software-Defined Networking Open Source?

No, Software Defined Networking in itself is not open source.

Although both allow for open networking, they are not the same thing. This misconception arises when we consider the OpenFlow protocol, the initial key to the creation of SDN. While this protocol is a type of open-source software, not all SDN networks allow for open networking. SDN can also be done in a more limited environment, without open networking. So, SDN itself is not open source. But both open source and SDN play a combined role in open networking.