A building automation and control network (BACnet) master-slave/token-passing (MS/TP) automatic media access control (MAC) addressing system having a BACnet MS/TP network, a MAC assigner on the network, and one or more MAC assignees on the network. Each assignee may have a global unique identity (GUID) and the assigner may have a pre-defined address. The assigner may gather virtually all GUIDs of the MAC assignees on the network and gather virtually all unused MAC addresses on the network. The assigner may map GUIDs to the unused MAC addresses and send a resulting map to the MAC assignees for assignment of a MAC address to each assignee. Each assignee may be assigned a MAC address according to its GUID, and the assignment of a MAC address to each assignee may occur automatically without manual intervention. In other words, the system may provide auto MAC addressing.