3Com 8800 Configuration Manual page 540

3Com Switch 8800 Configuration Guide Chapter 38 MSTP Region-configuration
Figure 38-3 BPDU packet format
Figure 38-4 MSTI information format of the last part in BPDU packets
Besides field root bridge priority, root path cost, local bridge priority and port priority, the
field flags which takes one byte in an instance is also used for role selection. The
following figure describes the meaning of its eight bits:
38-5