This read-write integer sets the VLAN tag used for the device's system-wide 802.1X monitoring mode, a mode used to observe authentication activity without actually enforcing access control, with 0 disabling the feature. An administrator sets this when rolling out 802.1X in a non-disruptive monitor mode to see how clients would authenticate before switching to full enforcement. For example, setting this OID to a dedicated monitoring VLAN lets the admin review real authentication attempts and results for weeks before flipping the switch to fully enforce 802.1X access control.