Allied Telesis AT-8100 Series - Manual (Page 784)

Chapter 53: STP, RSTP and MSTP Protocols
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Determining whether a bridge port is point-to-point, edge, or both, can be
a bit confusing. For that reason, do not change the default values for this
RSTP feature unless you have a good grasp of the concept. In most
cases, the default values work well.