Which IPSec Mode is the Most Secure for Remote User Access?

A.

In both ESP and AH cases with IPSec Transport mode, the IP header is exposed.

The IP header is not exposed in IPSec Tunnel mode.

The most secure IPSec mode for an organization to implement for remote user access would be Tunnel mode (option A).

IPSec (Internet Protocol Security) is a set of protocols used to secure internet communications, including VPNs (Virtual Private Networks). IPSec provides encryption, authentication, and integrity protection for data transmitted over the internet. It can operate in two modes: tunnel mode and transport mode.

Tunnel mode is the preferred choice for VPNs because it encrypts the entire IP packet, including the original IP header and payload, and encapsulates it within a new IP packet. This provides end-to-end encryption and protects against attacks such as IP spoofing and packet sniffing.

Transport mode, on the other hand, only encrypts the payload of the IP packet and leaves the original IP header intact. This mode is often used for communication between two hosts within a network, rather than between networks.

AH (Authentication Header) and ESP (Encapsulating Security Payload) are two protocols used in IPSec to provide authentication and encryption, respectively. AH-only mode (option C) would provide authentication but no encryption, making it less secure than Tunnel mode. ESP-only mode (option D) would provide encryption but no authentication, leaving the connection vulnerable to attacks such as man-in-the-middle.

In summary, Tunnel mode provides the highest level of security for VPNs, as it encrypts the entire IP packet and encapsulates it within a new packet, while also providing authentication and integrity protection. Therefore, option A is the correct answer.