The network that is located between the public Internet and the company's internal network is known as:

IPSec is a protocol suite used to authenticate and encrypt IP packets, not a network segment or topology concept.

A VPN creates an encrypted tunnel over a public network to allow remote access, but it does not describe a network zone positioned between the Internet and an internal network.

An intranet is a private network accessible only to an organization's members, which describes the internal network itself rather than the buffer zone in front of it.

A DMZ is a network segment that sits between an untrusted external network (the Internet) and a trusted internal network, typically enforced by firewalls on both sides. It hosts public-facing services like web or mail servers while shielding the internal network from direct external access. This isolation limits attack surface by ensuring that a compromised DMZ host cannot directly reach internal resources.