This read-write bitmap lists which switch ports are permitted to become members of the configured 802.1X guest VLAN when a connected client fails or skips authentication. An administrator sets this to scope the guest VLAN feature to specific ports, such as public-facing access ports, while excluding trusted uplinks or server ports. For example, an admin would include only the lobby and conference-room ports in this bitmap so unauthenticated laptops there fall into the guest VLAN, while server-room ports are left out.