Final answer:
The IPsec protocol that ensures integrity protection and user authentication without encrypting the data payload is Authentication Header (AH). AH provides a checksum to verify data integrity but does not conceal the payload content.
Step-by-step explanation:
The IPsec protocol that provides integrity protection for packet headers, data, and user authentication but does not encrypt the data load is Authentication Header (AH). Unlike Encapsulating Security Payload (ESP), which provides both integrity and encryption AH is exclusively concerned with ensuring the integrity and authenticity of the data.
It works by attaching an additional header to each packet which includes a checksum that can be used to verify that the contents have not been altered in transit. However, because it does not encrypt the payload, the data within the packet remains readable to anyone who intercepts the packet.