What Is SD-WAN (SDWAN), and What It Cannot Do
SD-WAN, often written SDWAN, stands for software-defined wide area network. It joins an organisation's sites across ordinary internet connections, using software at each site to build encrypted tunnels and choose between links. It is widely marketed as the successor to MPLS. This guide explains what it is, what it does well and what it cannot do.
SD-WAN meaning, in plain terms
An SD-WAN puts an appliance, physical or virtual, at every site. Each site has one or more internet connections, often from different providers. The appliances build encrypted tunnels to each other across those connections, measure how each tunnel is performing, and send each kind of traffic down whichever looks best at the time. A central controller holds the policy and pushes it to every site.
The network between the sites is still the internet. SD-WAN is an overlay: it manages how traffic is sent across connections it does not own or control.
What SD-WAN does, and what it does not
| SD-WAN can | SD-WAN cannot |
|---|---|
| Encrypt traffic between sites across the internet | Keep that traffic off the internet |
| Measure several links and choose the better one | Improve a link, or the internet paths beyond it |
| Fail over to a second connection if one exists | Create resilience where both links share a duct, cable or exchange |
| Apply policy centrally across the estate | Remove the appliance and licence needed at every site |
| Combine connections from many local providers | Make one provider accountable for the whole path |
Where SD-WAN fits
SD-WAN suits estates of many small sites that mainly need internet access, where cloud applications are reached over the internet anyway and sites exchange little traffic with each other. It can also join connections from many local providers in places one network cannot reach. Where the lowest cost per site matters more than predictable performance between sites, those are reasonable trade-offs.
Where it falls short
Organisations whose sites depend on shared systems, voice and each other need something different from their WAN: privacy that does not depend on configuration at every site, predictable performance between locations, and one provider responsible when something goes wrong. Those are properties of a private MPLS network, and they are exactly what an internet overlay cannot add. We set out the comparison in MPLS vs SD-WAN, and what an MPLS network is in what is MPLS.
If you are already being asked to move from MPLS to SD-WAN, the questions to ask before you migrate are worth answering first.
Common questions
What does SD-WAN stand for?
SD-WAN, also written SDWAN, stands for software-defined wide area network: software at each site that builds encrypted tunnels across internet connections and chooses between them.
Is SD-WAN the same as MPLS?
No. MPLS is a private network operated by a provider, which keeps traffic between sites off the internet. SD-WAN is an overlay that sends traffic between sites across the internet inside encrypted tunnels.
Does SD-WAN replace MPLS?
It is often sold that way, but it replaces a private network with tunnels across the internet. For organisations whose sites depend on shared systems and voice, a private MPLS WAN usually remains the better choice.
Can SD-WAN fix a poor internet connection?
No. SD-WAN can move traffic to a better link if one exists, but it cannot repair a poor line or add capacity the line does not have.
Does Netavo provide SD-WAN?
No. Netavo provides private MPLS WANs on its own core network, which it considers the better choice for most multi-site organisations.
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