This value, carried in OpenFlow connection notifications, is the datapath's unique identifier, where the lower 48 bits are a MAC address and the upper 16 bits are vendor/implementer-defined. Admins use this ID because it is how an OpenFlow controller uniquely identifies and addresses this specific switch's forwarding datapath among potentially many switches under its control. For example, a controller's topology view would list switches by this datapath ID, letting an admin match a controller-side flow table entry back to the physical switch reporting this connection entry.