WAN and SD-WAN Architecture
WAN and SD-WAN Architecture
A solid grasp of WAN and SD-WAN architecture is foundational for the Arista ACE Specialist - WAN Routing exam. You must understand the evolution from traditional hub-and-spoke WANs to modern SD-WAN solutions, including the separation of control and data planes, the role of overlay tunnels, and the concept of a fabric. Key components include the SD-WAN controller (often called a director or orchestrator), edge devices, and the underlay transport networks (MPLS, Internet, LTE). Arista’s SD-WAN solution, CloudVision Pathfinder, integrates with Arista’s EOS and CloudVision to provide centralized management and policy enforcement.
Candidates should be able to differentiate between underlay and overlay networks, explain how SD-WAN provides dynamic path selection, and describe high-availability designs such as active-active and active-standby. Traps often involve confusing the roles of the controller and orchestrator, or misunderstanding where policy is enforced (at the edge vs. the controller). Another common pitfall is assuming that SD-WAN requires a specific transport; in reality, it is transport-agnostic.
Worked example / rule of thumb: Remember that in SD-WAN, the control plane is centralized (controller) while the data plane remains distributed (edge devices). This separation allows for centralized policy but distributed forwarding. When designing, always consider that the underlay must be IP reachable and that overlay tunnels are established between edges, not to the controller.
Key points:
- SD-WAN separates control plane (centralized) from data plane (distributed).
- Overlay tunnels (e.g., VXLAN, IPsec) run over any underlay transport.
- Arista’s SD-WAN solution leverages CloudVision for orchestration and Pathfinder for path selection.
- High availability can be achieved with redundant controllers and edge devices.
- Policy is enforced at the edge, not at the controller.