A Demilitarized Zone (DMZ) is a network segment that acts as a buffer zone between the internal network and untrusted networks, such as the internet. It is used to host systems that must be accessible from both internal and external networks but should not provide a direct route to the internal network. By placing legacy systems that require external access within a DMZ and allowing only specific, necessary communication, the organization can maintain tight security over these connections, reducing exposure to potential threats.

A VLAN is useful for segmenting the internal network but does not specifically cater to the safe handling of external communications. Data Loss Prevention (DLP) is important for protecting sensitive information from leaving the network but does not fundamentally address the regulation of communication channels with external partners. A NAC solution focuses on regulating access to the network by devices and users within the organization, rather than managing the flow of network traffic to and from external connections.