By default, a switch operates in Per-VLAN Spanning Tree Plus (PVST+) mode using traditional 802.1D STP. Therefore, RSTP cannot be used until a different spanning-tree mode (MST or RPVST+) is enabled. Remember that RSTP is just the underlying mechanism that a spanning-tree mode can use to detect topology changes and converge a network into a loop-free topology.
The only configuration changes related to RSTP affect the port or link type. The link type is used to determine how a switch negotiates topology information with its neighbors.
To configure a port as an RSTP edge port, use the following interface configuration command:
Switch(config-if)# spanning-tree portfast You already should be familiar with this command from the 802.1D STP configuration. After PortFast is enabled, the port is considered to have only one host and is positioned at the edge of the network.
By default, RSTP automatically decides that a port is a point-to-point link if it is operating in full-duplex mode. Ports connecting to other switches are usually full duplex because there are only two switches on the link. However, you can override the automatic determination, if needed. For example, a port connecting to one other switch might be operating at half duplex, for some reason. To force the port to act as a point-to-point link, use the following interface configuration command:
Switch(config-if)# spanning-tree link-type point-to-point
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