Which protocol should a network administrator use to ensure integrity encryption and authentication for a site-to-site VPN utilizing IPSec?

In a site-to-site VPN utilizing IPSec, the most effective protocol for ensuring integrity, encryption, and authentication is the Encapsulating Security Payload (ESP).

ESP is a core component of the IPSec suite that not only provides confidentiality through encryption but also ensures the integrity and authenticity of the data being transmitted. It does so by encapsulating the original data packets and adding headers and trailers that include integrity checks and encryption techniques. This holistic approach makes it a robust option for secure communications over potentially untrusted networks.

On the other hand, while Authentication Header (AH) is also part of the IPSec protocol suite, it does not provide encryption, only integrity and authentication. This makes AH less suitable for scenarios where confidentiality is required. The other options, such as EDR and DNSSEC, serve different purposes related to endpoint detection and DNS security, respectively, and are not relevant in the specific context of establishing a secure site-to-site VPN with IPSec.

Therefore, ESP is the correct choice when securing communications in a site-to-site VPN scenario, as it fulfills all necessary requirements of integrity, encryption, and authentication.