Which protocol is commonly used for securing remote access connections?

IPSec is a protocol suite that is widely recognized for securing remote access connections because it provides strong authentication, integrity, and encryption for IP packets during communication between devices over an unsecured network, such as the internet. It operates at the network layer and is often used to create Virtual Private Networks (VPNs), which allow users to access a private network securely from a remote location.

This protocol works by establishing a secure tunnel between the client and the server, ensuring that all data transmitted is encrypted and protected from eavesdropping or tampering. The versatility of IPSec also allows it to be used in different modes, such as transport mode and tunnel mode, catering to various networking needs.

In contrast, other options do not serve the same primary purpose of securing remote access connections. For example, PPTP primarily offers a method for creating VPNs but lacks the robust security features provided by IPSec. On the other hand, SMTP and FTP are protocols designed for sending emails and transferring files, respectively, and they do not include inherent security mechanisms to protect connections against interception or unauthorized access.