This read-only octet string is the bridge's unique spanning-tree identifier, composed of a two-byte priority value followed by the six-byte Ethernet MAC address of the bridge. An admin uses this value to recognize this specific bridge when comparing spanning tree topology data across multiple bridges on the network, since it must be unique network-wide. For example, comparing bdgdeviceBridgeID against bdgdeviceDesigRoot lets the admin determine whether this bridge is itself the root of the spanning tree or is deferring to another bridge.