Underlay

An Underlay is the underlying network infrastructure that transports data between physical network devices and endpoints. It typically consists of switches, routers, physical connections and routing protocols that provide the required IP connectivity. Virtual Overlay networks can be built on top of this infrastructure using technologies such as VXLAN or EVPN. While the Underlay provides reliable reachability between participating network components, the Overlay creates an additional logical network structure above it. Underlay networks are particularly relevant in data centres, cloud infrastructures and Software-Defined Networking environments. A stable and high-performance Underlay infrastructure is essential because failures, packet loss or routing issues at this level can also affect the Overlay networks operating above it.