SD-WAN – What is it?


SD-WAN. What is it? Should I care? Is it a standard? Why would I want to software define my WAN?! Let’s get to it…


You would have seen or heard SD-WAN if you work in IT, it is a hot topic and honestly, it has many definitions which can be confusing. SD-WAN is not a standard, so vendors and providers use it as a marketing term. I want to demystify the marketing with this post.


SD-WAN is an evolution in branch connectivity. It is intelligence at the edge of the network to leverage multiple links, load balance and monitor the performance of each, as well as application awareness. The technology is built into appliances, which there are many! Ok, yes, that was basically marketing, let me break it down.


If you think about your WAN currently, it is likely a mix of direct internet access (DIA), ADSL, 4G, MPLS, IPSsec VPNs… there are so many ways to connect! You may also have different edge devices too, a router, firewall, or from a switch. You will also have a process to handle a connectivity failure at a site. One of the challenges with office connectivity, or building a WAN, is resilience. There are many ways to achieve this, both physically and logically. A backup circuit, IP SLA, or a floating static route, some of these solutions are complex and over-engineered.


One of the features of SD-WAN overcomes this problem. Utilising all of the links available at a site, with real-time monitoring of each and steering traffic down the ‘best’ for specific types of traffic. For example, which of my available links is the best for voice traffic? Which has the lowest latency to a destination? and so on… the devices are constantly probing the links to determine the best – insight into the quality of the link. It challenges circuit failover as all the links are in use, but you can  achieve sub-second failover for your IPSsec VPN.


SD-WAN appliances are also application/layer 7 aware. This means you have even more control to steer traffic, which of my available links is the best, lowest latency to Office365? As more and more applications move to the cloud, you realise why SD-WAN has so much traction.


However, arguably the main reason why SD-WAN is such a hot topic, is cost. You can significantly reduce WAN spend by deploying an SD-WAN solution, because instead of paying for expensive links, with SLAs, you can replace them with commodity/consumer links. This is also the reason it is compared with MPLS, they are very different offerings but ultimately, you will be able to connect and office for less with SD-WAN, when compared with MPLS.


I hope that has helped you understand SD-WAN, a very brief overview! I will write a follow up. We will deep dive into SD-WAN vs MPLS at a lower level, I’ll also go through SD-WAN deployments/topologies, as well as the appliance offerings!