SD-WAN. All it is.

March 26, 2019

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By Kevin Prater, Kovarus, Practice Manager Collaboration / Network Edge

SD-WAN is one of the top buzz words/phrases/acronyms buzzing around the heads of CIOs, IT Directors and Network Managers today. It seems like we hear about it all day, every day and for good reason; it really makes sense and there’s a lot it can do for you. Some of the WAN concerns it addresses include:

  • Efficiency
    • Are you dealing with multiple circuits/transport types and need better manageability and utilization? Circuits sitting idle?
    • Are your WAN costs too high and are you looking at less expensive circuit options?
  • Experience
    • Do you need better visibility and/or analytics into your applications and network resources, so you know what’s going on?
    • Do you need a more reliable experience for applications?
  • Security
    • Do you have audit and compliance requirements you need to address?
    • Can you ensure security over an insecure transport?

But what I’ve recently opened my eyes to is how difficult some seem to make it when they start talking about it. Some are misinformed, some confused, and some talk in circles as big as you’d find in a Nebraska corn field.

Let’s cut through all the marketing value-added messaging for just a second to quickly get to the essence of what SD-WAN is from an architecture perspective.

A Little History First

It might help if we think about traditional networking for a minute — a typical Layer-3 switch for example. What does it consist of and what’s really going on there?

Well, first let’s talk about traffic, and we’ve got a couple of broad types. We’ve got routing traffic and routed traffic. We’re making a distinction because of the way each are treated and by whom.

  • Routing Traffic
    Routing traffic is your protocol traffic, it’s your routing tables, your topology information, neighbor relationships with other routers, updates about your network as a whole. It’s all the stuff used to build out a real-time, up-to-date map to get your routed traffic (data) where it needs to go.
  • Routed Traffic
    Well, I’ve already spilled the beans haven’t I; this is your data. All the traffic that needs to get from point A to point B. I sit at my PC and send an email with a crazy cat video to my buddy; that’s routed traffic.

Great! So now we know there are essentially two types of traffic, now what?

Let’s go back to our Layer-3 switch. Our switch has a couple of different parts. It’s a chassis with some power supplies and fans and a couple of different types of modules in it. It’ll have at least one (if not two) supervisor modules and then some I/O modules for our network stuff to plug in to. Now if we break it down even further, we’ve really just got a couple of different communication planes over which our different traffic types (routing and routed) bounce around. These planes are the Control Plane and the Data Plane.

  • Control Plane
    As you’ve guessed by now, the Control Plane is where the decisions are made on how to control your data, right? This is your supervisor module; you can have one, or two for redundancy. The control plane deals with routing protocol stuff, updates, keepalives, neighbor relationships, network convergence and building tables like the Routing Information Base (RIB) for instance. The RIB is the map your routing engine uses to send your data on its way.

Control traffic = Routing traffic.

  • Data Plane
    The data plane is where your stuff (cat video) lives … well mostly. It’s where it begins and ends at least. This is your I/O module and it spends its time forwarding and switching packets. Your data comes into the switch on a port in the I/O module (data plane), the data plane then forwards that traffic to the destination or to the next hop. If the destination is local, the traffic is forwarded to the appropriate local port. If not, it’s forwarded to the control plane where a routing determination is made.

Data Plane traffic = Routed traffic.

C’mon, What Is It?

So, in a Layer-3 switch like we’re talking about, it’s typically a chassis with these modules plugged into it. The backplane that these modules are plugged into makes all the connections needed for these two different pieces hardware to be able to communicate. This creates a switch fabric if you will, over which these different planes can communicate.

Are you with me? Cuz that’s it!

At its core, SD-WAN is really this architecture, blown up and spread across whatever geography you’d like. Let’s connect the dots:

SD-WAN Data Plane

  • These are your SD-WAN edge devices
    • Depending on the vendor, it may be:
      • An appliance
      • Software on a router
      • Software on a firewall
      • VM
  • It’s taking data plane traffic, making forwarding decisions and spitting it out

SD-WAN Control Plane

  • Handles control (routing) traffic
  • SD-WAN controllers live here and they:
    • Keep track of edge devices
    • Keep track of push policies
    • Maintain a VPN overlay topology
      • Sometimes full-mesh, sometimes hub and spoke, you can tune it to your environment and needs
  • There’s also typically a management and/or orchestration component here that provides:
    • A GUI interface
    • Dashboards for monitoring, analytics, policy creation, etc.

SD-WAN Fabric

That’s your WAN! Whether it’s MPLS, Broadband Internet, LTE, it doesn’t matter. Your WAN is the fabric over which these two planes communicate.

So, while it’s really just a software defined version of what we’ve been doing at Layer-3 for years, this fresh approach at the architecture nails 3 big WAN concerns organizations are dealing with:

  • Efficiency
    • You get better manageability through centralized polices and control
    • You get better utilization — Things like dynamically routing the traffic chooses the best path for application data so backup circuits don’t have to sit idle
    • Gives you the opportunity to entertain less expensive circuit options, it no longer matters what the circuit is
  • Experience
    • Gives you application visibility and analytics so you really know what’s going on with your application traffic
    • Provides for a consistent application experience regardless of where your user is located
  • Security
    • Helps address audit and compliance requirements you may have
    • Helps ensure security over an insecure transport (internet)

I started this post poking fun of the marketecture only because it can be easy to get caught up in it and start overthinking the solution. Hopefully this illustrates that, at its core, SD-WAN is a pretty straightforward concept and can provide a ton of value to your organization.

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