New Values for Ports Bandwidth (Mbps)

In legacy STP, the BID field was composed of 2-byte priority plus 6-byte MAC address. Because 802.1t steals 12 bits from the priority field to compose the VLAN number, the priority field can now only take 16 values by increments of 4096. The new BID is as follows:

BID = Priority (4 bits) + VLAN number (12 bits) + MAC (6 bytes)