3Com 3500 manual Management CFM. In a single MAC node, Port B has precedence with defaults for

226CHAPTER 8: FIBER DISTRIBUTED DATA INTERFACE (FDDI)

This
Connection
Is Rejected	If This Bit Is Set	Connection Rules
A-M	3	Tree connection with possible redundancy. The
		node may not go to Thru state in Configuration
		Management (CFM). In a single MAC node,
		Port B has precedence (with defaults) for
		connecting to a Port M.
B-A	4	Normal trunk ring peer connection.
B-B	5	Undesirable peer connection that creates
		twisted primary and secondary rings; notify
		SMT.
B-S	6	Undesirable peer connection that creates a
		wrapped ring; notify SMT.
B-M	7	Tree connection with possible redundancy. The
		node may not go to Thru state in CFM.
		In a single MAC node, Port B has precedence
		(with defaults) for connecting to a Port M.
M-A	12	Tree connection with possible redundancy.
M-B	13	Tree connection with possible redundancy.
M-S	14	Normal tree connection.
M-M	15	Connection that allows one system port to be
		connected to another system port.