SD-WAN & Traditional WAN
Like anything else, not all WANs are created equal. Choosing the right WAN for an organization means vetting its needs against what it’s operationally capable of. We will be discussing some of the fundamentals of how traditional WANs work compared to how the software-defined WANs operate in the following:
How Traditional WAN Work
Traditional WANs worked through the purchase and installation of proprietary circuits to route IP services to their intended clients. This is done with layers of underlying hardware in order to complete networks in their entirety. The scope of these types of networks makes management for IT teams a cumbersome and laborious effort due to the number of hardware devices install and processes necessary to manage network activity.
- Security is normally handled in the form of IP blocklists and access control lists to prevent malicious traffic from infiltrating the network. This is all centrally managed from hardware routers and associated applications.
- Setting up additional branch offices and remote locations would require additional hardware, which in turn drives up costs for businesses.
Scaling traditional WANs is more difficult compared to SD-WANs. This is because extensive planning would have to do in advance along with getting the required logistical support in place to set up the infrastructure necessary to get operations up and running.
How SD-WAN Work
SD-WANs work by utilizing tunneling solutions on pre-existing network architecture. It’s basically operating a network on top of a network, where communications paths are unified and application performance is optimized. It gives enterprises the option of dynamically connecting branch offices and the HQ office by leveraging internet and cloud capabilities along with integrated intelligence. This makes software-defined networks much easier to deploy regionally and globally.
The software-defined WAN architecture has several advantages that the traditional WAN lacks. Some of the advantages include:
- Leveraging cloud and internet capabilities to manage traffic between the headquarters/corporate office and its subsidiaries.
- Zoning of different branch offices via the utilization of hybrid WAN + LAN concepts and network segmentation.
- Shorter deployment times where originally it would have taken advance planning and logistical support to deploy a vast network covering a large area.
What is the Difference Between WAN and SD-WAN
We have placed a side-by-side comparison of traditional WANs to SD-WANs, so they give you a greater context as to how they operate:
| Traditional WAN | SD-WAN |
| Distributed Configurations: Network configurations are housed locally on individual routers and are usually based off of a template. |
Simplified Branch Services: The software-defined approach offers flexibility that is not prevalent in traditional WANs. |
| Failover depends on the state of the link, which forces users to depend on routing protocols | Cloud-first: Services that are already positioned in the cloud will be given prioritization. |
| Device policies have to be individually configured on a per-device basis in order to be compliant. | Application prioritization: Places quality of service and prioritizes WAN applications across the board. Provides real-time traffic monitoring in the event of brownouts, and does not wait for up/down statuses of links prior to initiating a switchover to alternate carrier links. |
| Lead time will be needed in order to set up new networks at different branch offices, which usually requires months of planning in advance prior to deployment. | Lower operational costs: SD-WANs place greater emphasis on the use of low cost, high-speed connectivity. While taking advantage of connection options such as DSL or broadband, this allows for the elimination of MPLS circuits. Businesses still have the option of using MPLS circuits prior to transitioning out completely in phases. |
| Heavily dependent on data centers, forcing traffic to be backhauled through the data centers and clog traffic. | WAN virtualization: SD-WANs have a unified bandwidth pool provided by multiple service providers. This allows for greater network resource utilization when data migrates through between offices. |
| Data centers are limited in their capacity to deal with incoming connections to multiple cloud platforms. | SD-WANs are not restricted based on the limitations of underlying hardware that comprises the network. |
As you can see from the comparison, the software-defined approach leverages capabilities within the internet and the cloud that traditional networks cannot do.
SD-WAN vs. Traditional WAN Total Cost of Ownership
The total cost of ownership (TCO) for SD-WAN versus traditional WAN should include more than circuit costs. A practical comparison should evaluate WAN circuits, appliances, software licensing, deployment, administration, maintenance, upgrades, and technical support over the expected lifecycle.
| TCO factor | Traditional WAN | SD-WAN |
| WAN circuits | Often relies heavily on higher-cost MPLS or private circuits | Can combine broadband, DIA, LTE/5G, MPLS, and other transports |
| Appliances | Routers and related hardware at each site | SD-WAN edge devices or compatible virtual appliances |
| Licensing | Router and feature licenses may apply | SD-WAN platform, security, analytics, and feature subscriptions may apply |
| Deployment | Manual configuration and site-by-site provisioning | Centralized policies and automated provisioning can reduce deployment effort |
| Administration | More device-level management | Centralized orchestration and policy management |
| Maintenance | Hardware maintenance and configuration management | Hardware plus SD-WAN platform maintenance and subscription costs |
| Upgrades | Often requires individual device changes | Centralized software and policy updates can simplify upgrades |
| Support | Router, circuit, and network-support costs | SD-WAN vendor, connectivity, hardware, and managed-support costs |
The resulting TCO depends on the organization’s network size, traffic requirements, existing contracts, hardware lifecycle, and management model. SD-WAN may reduce overall TCO by using lower-cost transport and simplifying operations, but include licensing, edge hardware, deployment, and ongoing subscription costs for an accurate comparison.
Does SD-WAN Require Replacing Existing WAN Infrastructure?
No. SD-WAN does not necessarily require replacing existing WAN infrastructure. It can be deployed as an overlay on existing connectivity, allowing organizations to keep MPLS, existing routers, broadband, DIA, or other WAN transports while adding SD-WAN capabilities.
A brownfield SD-WAN deployment can start with selected sites or applications while existing routers and MPLS circuits remain operational. Organizations can then migrate traffic and sites in phases, gradually replacing legacy infrastructure only when needed. This approach reduces disruption, supports coexistence during the transition, and allows businesses to move toward a fully SD-WAN-based architecture over time.
Does SD-WAN Work Without an Internet Connection?
Yes. SD-WAN does not inherently require an internet connection because it is designed to operate over different network underlays. Depending on the deployment, SD-WAN can use broadband internet, dedicated internet access (DIA), LTE/5G, MPLS, or a combination of these transports.
For example, an organization can use MPLS as the primary underlay and LTE/5G as a backup, or combine broadband, DIA, and MPLS across different sites. SD-WAN creates and manages secure overlays across the available connections, automatically selecting paths based on application requirements, network conditions, and configured policies. Therefore, SD-WAN is transport-independent rather than internet-dependent, although many SD-WAN deployments use internet connectivity because it is widely available and cost-effective.
