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SD-WAN architecture is a policy-controlled network overlay that connects sites across one or more underlying WAN transports. Central systems distribute configuration, routes and traffic policies; edge devices at sites use those policies to forward traffic. There is no single required SD-WAN topology or deployment form: the right design depends on how sites communicate, where services run and who operates the network.
How SD-WAN architecture works
SD-WAN applies software-defined networking concepts to the wide area network. Its logical overlay sits above the physical or virtual transport network, allowing network policy and traffic steering to be managed across connected locations rather than configured independently at each site.
Underlay and overlay
The underlay is the set of WAN connections that carry traffic, such as Internet, MPLS or mobile links. The overlay is the logical fabric established across those connections between SD-WAN edge devices. A site may use one transport or several; the edge can select a path according to application policy and measured link conditions.
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Edges can be deployed at branches, campuses, data centers and cloud environments. They forward user traffic, while centralized functions help configure the network and distribute topology, routing and policy information.
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Four functional planes
Cisco documentation presents a useful conceptual model that separates SD-WAN responsibilities into four planes. These are functional categories, not a universally mandated component list; vendors may combine or divide them differently.
| Plane | Primary responsibility |
|---|---|
| Orchestration | Assists with device authentication and onboarding. |
| Management | Provides centralized configuration, monitoring and maintenance. |
| Control | Builds and maintains the overlay topology and distributes route and policy information. |
| Data | Forwards packets between WAN edge devices. |
Cisco Catalyst SD-WAN as one implementation
In Cisco Catalyst SD-WAN, the named components are SD-WAN Manager for management, SD-WAN Controller for control, SD-WAN Validator for orchestration and WAN Edge devices for data forwarding. Cisco describes the Overlay Management Protocol (OMP) as carrying overlay control information. These names and protocol details apply to Cisco’s implementation; they should not be treated as universal SD-WAN terminology.
What SD-WAN topology types are available?
Topology describes how sites connect through the overlay. The main choice is whether traffic should pass through central hubs, use direct site-to-site paths or combine the two patterns.
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Hub-and-spoke
In a hub-and-spoke topology, branch sites (spokes) connect through one or more hubs. This can simplify centralized access to shared services and provide a clear point for applying controls. Branch-to-branch traffic may need to travel through a hub, so the design should account for the resulting path and latency.
Full mesh
A full mesh gives sites direct overlay paths to one another. It can avoid sending branch-to-branch traffic through a central hub, but increases the number of potential site relationships and can add design and operational complexity as the network grows.
Regional or partial mesh
A regional or partial mesh combines direct paths for selected sites with hub-based connectivity for others. It can match regional traffic patterns or service locations without requiring every site to connect directly to every other site.
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These topologies are trade-offs rather than a universal ranking. Cisco and Versa guidance describes topology options; the practical choice depends on traffic flows, latency needs, network scale, resilience requirements, operational capacity and where inspection or other services must take place.
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Deployment form is not the same as operating model
Two separate decisions shape an SD-WAN service: where its components run and who operates them. Fortinet describes physical, virtual and cloud deployment options as well as DIY, managed and co-managed models.
| Decision | Options | What it determines |
|---|---|---|
| Deployment form | Physical appliance, virtual appliance, cloud deployment, or a combination | Where SD-WAN edge or service components run. Cloud options can include cloud or multi-cloud use and cloud-plus-backbone approaches. |
| Operating model | DIY, managed service or co-managed service | Who configures, monitors and supports the network, and how those responsibilities are divided. |
A physical edge appliance does not imply that the customer must manage every network function, and a cloud deployment does not by itself establish that a provider operates the service. Confirm the actual responsibility split for configuration, monitoring, maintenance and support.
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What SD-WAN is used for
SD-WAN is designed for networks that connect distributed locations and need centrally coordinated policy across multiple WAN paths. Documented use cases include:
- Connecting branches, campuses and data centers with cloud environments.
- Steering application traffic across available WAN transports.
- Supporting SaaS and other cloud access patterns.
- Applying centralized policy and improving visibility across sites.
- Using segmentation or service insertion when the design requires them.
Cisco’s design guidance also identifies application recognition and visibility, real-time service-level policy, SaaS optimization, analytics, troubleshooting and resource planning as capabilities or use cases. These describe what a design may support, not independently measured outcomes. The result depends on implementation, applications, available links, policies and vendor features.
Potential benefits and their limits
Centralized configuration and monitoring can reduce the need to manage each site in isolation. Application-aware path selection can let policy respond to link measurements, while analytics and shared visibility may help teams investigate network behavior. These are potential operational benefits, not guarantees of lower cost, better performance or higher uptime.
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Actual results depend on whether the available transports meet application requirements, how accurately policies reflect those requirements, and how the network is implemented and operated. SD-WAN can select among available paths; it cannot make an underperforming transport meet a requirement it is unable to support.
Security considerations
An SD-WAN overlay is not, by itself, proof that a network is secure. Cisco’s security documentation describes authenticated control components and data-plane traffic carried in IPsec connections, using authentication, encryption and integrity mechanisms. Those details describe documented Cisco capabilities, not a guarantee that every SD-WAN product or configuration behaves identically.
Evaluate the security design across the whole deployment, including:
- How devices and users are identified and onboarded.
- How configuration changes are controlled and software is maintained.
- How traffic is segmented and which paths receive inspection.
- Where security services are located and how service insertion works.
- How encrypted paths, policies and exceptions are monitored.
How to assess an SD-WAN design
Compare designs against actual network requirements rather than the architecture label alone. Use these questions to structure an evaluation:
- Map traffic patterns. Identify which sites exchange traffic, which applications are most sensitive to latency or loss, and where cloud and shared services are located.
- Select a topology. Decide which flows need hub-based service access and which could benefit from direct paths; consider scale, resilience and operational complexity.
- Confirm deployment form. Establish which components will be physical, virtual or cloud-hosted and where network and security services will run.
- Define path policy. List available transports, application requirements, the link conditions used for steering and the expected failover behavior.
- Specify security controls. Document identity and onboarding, segmentation, encryption, inspection paths, service insertion and software maintenance responsibilities.
- Set operational ownership. Clarify who provisions devices, changes policy, monitors analytics, troubleshoots incidents and provides support in a DIY, managed or co-managed arrangement.
Vendor feature names, compatibility, commands and licensing can vary by release and product. Confirm those details in the applicable product documentation before using them in a production design.
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