AC-SYSTEM-MIB::acSys802dot1xMode is an integer that selects the port-based network access control method: 0 (disabled), 1 (EAP-MD5), 2 (Protected EAP/PEAP), or 3 (EAP-TLS). Network engineers configure this to enforce authenticated access—only allowing devices with valid credentials to connect to a physical port on the network. A value of "3" requires the strongest authentication (certificate-based TLS), which is preferred for high-security environments.