Overlays vs Underlays
Overlays are logical tunnelsEncapsulating one type of network protocol (called the payload protocol) within a different delivery protocol. A logical connection between two devices, in our case, two Silver Peak appliances. created for different traffic types and policies (such as VoIPVoice-Over-Internet-Protocol. A protocol optimized for the transmission of voice through the Internet or other packet-switched networks.).
UnderlaysThe physical transport network and its site-to-site connections, including MPLS networks, the Internet, LTE networks, or private lines. It also includes the tunnels built between Silver Peak appliances across any physical networks. are actual IPSecInternet Protocol Security Protocol. tunnels and physical paths taken (such as MPLSMultiProtocol Label Switching is an IETF initiative that integrates Layer 2 information into Layer 3 (IP) packets.).