System and method for performing automatic trunk formation in a multiple spanning tree protocol ("MSTP")-enabled bridge comprising a plurality of ports are described. In one embodiment, the method comprises determining which ones of the ports comprise MSTP trunk ports; forming an MSTP trunk group for each multiple spanning tree instance ("MSTI") comprising a group of Virtual Local Area Networks ("VLANs") belonging to the MSTI; and, for each of the MSTP trunk ports, determining whether a status of the MSTP trunk port is trunk active and if so, adding all VLANs in the MSTP trunk group of the MSTIs that are forwarding on the MSTP trunk port as tagged members of the MSTP trunk port.