The networking concept of “Underlay” refers to the physical network layer that provides the connectivity and transport for the overlay network, which is the virtual network layer that runs on top of the underlay network1. The underlay network is composed of routers, switches, links, and protocols that enable the data transmission between different locations2. The underlay network is independent of the overlay network, meaning that it does not need to be aware of the network configuration, policies, or services of the overlay network3. Therefore, option A best describes the underlay network, while options B, C, and D are incorrect. References: 1: Nokia Bell Labs Distributed Cloud Networks, Unit 2: Cloud Technologies and Features, Topic: Underlay and Overlay Networks 2: Module by Module - Self Study Note Guide, DC2.2– Cloud Options 3: Underlay Network - an overview | ScienceDirect Topics, Overview