Overlay networks are virtualized logical networks that operate on underlay networks, which are physical networks such as routers and switches. Overlay networks not only reduce operating costs such as connecting and disconnecting physical lines and changing switch settings, but also enable cloud providers to provide VPN services and reduce equipment purchase costs.

ONUG, a community aiming to open networks, defines the 10 main requirements for SD-WAN technology as follows.

Multiple public and private WANs can be controlled from a remote environment in an Active-Active configuration
CPE can be provided in a physical / virtual environment on general hardware
A secure, hybrid design that outperforms degraded network quality at any network WAN or application transport layer, and allows dynamic control across public and private WAN boundaries specifically for application policy. Is
It is an application that enables real-time visualization, prioritization, and policy changes that are unavoidable in business operations for each different organizational hierarchy (security, corporate compliance).
A WAN environment with excellent availability and resilience for users
Supports L2 / L3 that can be directly interconnected with switches and routers
Visualize location, application, and VPN quality on the dashboard
Security information event management (network integrated log management)
Supports zero-touch provisioning
Certificate expiration management and reporting automation for FIPS 140-2

How SD WAN works