Techniques are disclosed that may allow a network device comprising multiple line cards that are each executing a spanning tree algorithm to appear as a single spanning tree protocol entity to other network devices within a bridged local area network (LAN). In one example, a method includes determining, via a first processor on a first card of a network device, a first superior local port on the first card, transmitting, from the first card to a second card of the network device, a data unit specifying the determined first superior local port, and determining, via a second processor on the second card, a superior port on the network device among the first superior local port and a second plurality of ports on the second card based on a second plurality of BPDUs received via the second plurality of ports.