Microsoft’s support of the IP Security (IPSec) standard was enhanced with the release of Windows Vista this year. For smaller organizations, IPSec could prove to be a cheap alternative to other network access control (NAC) technologies. The real power of IPSec is in its ability to protect managed Windows machines from non-managed machines by requiring authentication before network communications can occur between two hosts. In 2004, Microsoft deployed domain isolation using IPSec within its own enterprise network, protecting 200,000 systems.”]
Source: https://www.darkreading.com/analytics/tech-insight-microsoft-s-ipsec