Difference between Underlay Network and Overlay Network | Devops for Growth | Scoop.it
Network Overlays –

Network overlays is the latest solution to meet these demands, in fact, this technology can speed configuration of new or existing services.
Underlay Network –

Underlay Network is different from Underlay Network which IT industry has known for years. Underlay Network is physical infrastructure above which overlay network is built. It is the underlying network responsible for delivery of packets across networks.
Overlay Network –

An Overlay Network is a virtual network that is built on top of underlying network infrastructure (Underlay Network). Actually, “Underlay” provides a “service” to the overlay