Question:
What are the advantages/features on enabling ESP in Tunnel mode?
Features and Functionality for ESP Based Tunnel:
ESP (Encapsulating Security Payload) is a way to encapsulate and decapsulate packets inside of a UDP wrapper (port 4500) for traversing NATs.
Using it can improve the performance of UDP-streaming applications like VoIP. For more information on ESP, see RFCs 2406 and 3948 .