Which protocol provides authentication header functionalities in IPSec?

The protocol that provides authentication header functionalities in IPsec is the Authentication Header (AH). AH is specifically designed to provide integrity, data origin authentication, and non-repudiation by attaching an authentication header to the packet. This helps ensure that the data has not been tampered with during transmission and verifies that the data truly comes from the claimed sender.

AH operates at the network layer and provides protection for the entire packet, including the header and payload, but does not provide confidentiality. This is vital for environments where data integrity and authenticity are of utmost importance.

In contrast, while protocols like Encapsulating Security Payload (ESP) also play a role in IPsec for data protection, they focus primarily on providing both confidentiality and authentication, rather than solely on the authentication features provided by AH. Other protocols mentioned do not pertain to IPsec in the same context and do not serve the same purpose as the Authentication Header.