The Best SDN Example in 5 Minutes

Learn more about software-defined network with this clear SDN example

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This SDN example will help you understand what SDN is and how it can be implemented in various context. In fact, this article will show you multiple SDN examples that you can reference when you learn networking.

What is SDN?

Before we dive deeper into the SDN example, let’s start with a brief definition of SDN. You may know this already, but read it anyway: there are many different flavors of SDN out there, and it is important that we are on the same page on what we mean. Otherwise, you may get the examples on something different than what you expected.

A Software-Defined Network (SDN) is a network that the administrator can configure by declaring how he wants the whole network to be, rather than configuring individual devices.

In practice, this means that SDN is a network with many networking devices and one controller. The network engineer configures the controller, which then configures the network devices in turn. This paradigm, opposed to traditional networking, is called controller-based network.

You can learn more about SDN here.

SDN Example

SDN Example #1: VMware Network Virtualization

This is one of the earliest software-defined network that most enterprises used, so it is a good starting point for the SDN example as well. VMware is a leading provider of virtualization software. Originally, each physical server had to run its own OS and application, and if you wanted one more application you needed to buy one more physical server.

VMware changed this paradigm with virtual machines: the server runs a special OS by VMware, called ESX, and then you can spin up multiple virtual servers on top of the physical server. You manage all that through a centralized system, called the vCenter.

So far so good, but those virtual machines, or VMs, need to communicate with each other. And this is where the vSwitch comes into play: it is an abstract concept by VMware that acts as a physical switch and allows some machines to communicate with each other, while other don’t. You configure everything from the vCenter, and don’t have to configure each physical server manually.

This is not unique to VMware. There are other system and tools that allow for similar virtualization, like Oracle Virtual Box (you can run this on your PC for free), or Linux KVM. Since the virtual switch is something that you configure from the controller and it gets deployed to the physical server that needs it – without you selecting which ones – we can call it a valid SDN example.

SDN Example #2: Cisco Meraki, Ubiquiti

SDN is prominent in Wi-Fi networks, where it was introduced almost 20 years ago, before “SDN” was even a thing. It is no surprise that we need to have an SDN example about Wi-Fi, with two vendors: Cisco Meraki, and Ubiquiti. Even the more traditional Cisco WLC deserves the stage here.

Unlike a home network, where a single Wi-Fi router is typically enough, a large office or building will need multiple Wi-Fi Access Points (APs). We call them access points because they are points of access to the network through Wi-Fi: the AP is then physically cabled to the network, and allows Wi-Fi devices to access that network.

Unlike what some people think, a virtual world or virtual reality is not an SDN example
This is what people think when describing SDN. In reality, it is not so exciting and flashy.

A large building can require quite a lot of APs, and they often need to be configured in the same way: propagate the same network over the air (SSID), use the same authentication method, use the same frequencies, and so on. You can see that having a controller here is quite practical.

Traditionally, you had this controller running on a server in your Datacenter. This is the case of the Cisco Wireless LAN Controller (WLC). More recently, a cloud controller is also a possibility: Access Points register “in the cloud” over the Internet, you then access a web page and configure your network from there. This is how Cisco Meraki and Ubiquiti work. Even if the network is wireless, this is still a great SDN example.

SDN Example #3: SD-WAN

SD-WAN is short for Software-Defined WAN, or Wide-Area Network. Long story short, a WAN is the network that allows locations that are far away from each other to communicate. If it has a different postal address, then it is probably a location that will communicate over WAN.

Here, the potentiality of SDN starts to diminish because, in the end, you still need to run physical cables between your locations. However, in most cases all locations already have a public Internet connection that they can use. With SD-WAN, you can create virtual tunnels to have private communication between different sites. All your data will be encrypted and sent from one location to another as if they were directly connected.

At a physical level, all the tunnels need is Internet connectivity. You can then spin up as many tunnels as you want, create a hub-and-spoke model or a spoke-to-spoke (any to any) communication model. You can do all that defining it in software, so this is also a great SDN example.

SDN Example #4: VXLAN in the Datacenter

VXLAN is probably the greatest SDN example, because here the use case for SDN is incredibly strong. We can think of VXLAN as of VLANs taken to the extreme, but let’s go in order.

VLANs are a technology to have multiple logical domains across the same physical network. Network devices (switches) mark all the traffic coming from a device with a specific ID, the VLAN tag, so that the receiving switch can send that traffic only to devices that have the same tag. The problem is that this tag is applied at the data-link layer, in the ethernet protocol, which is not propagated across different subnets or IP ranges. So, you can use VLANs to virtualize a network within the same building (or, in case of the datacenter, within the same rack).

An SDN Example is what happens in the datacenter with VXlans
Advanced technologies such as machine learning are possible because large datacenters run VXLAN.

VXLANs changes this paradigm, they encapsulate al traffic into UDP packets, that run on-top of the network layer, and then add the tag here. As a result, we can now have a virtual network that is spread across multiple locations, even far away from each other.

This adds extreme complexity but flexibility as well. In fact, you can implement VXLAN directly into your hypervisor, the physical server running virtual machines, rather than on the physical network itself. You will need a controller for this, but since VXLAN is a standard protocol defined in RFC 7348, you are not tied to a specific vendor.

Summary of SDN Example

We didn’t give you just one, but multiple examples of SDN. Hopefully, you should have by now a clear idea of what software-defined networking is and have the SDN example that best suits you. Continue learning about networking with our free CCNA course.

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Alessandro Maggio

Project manager, critical-thinker, passionate about networking & coding. I believe that time is the most precious resource we have, and that technology can help us not to waste it. I founded with the same principle: I share what I learn so that you get value from it faster than I did.
Picture of Alessandro Maggio

Alessandro Maggio

Project manager, critical-thinker, passionate about networking & coding. I believe that time is the most precious resource we have, and that technology can help us not to waste it. I founded with the same principle: I share what I learn so that you get value from it faster than I did.

Alessandro Maggio


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