Difference between Spanning Tree Protocol (STP) and Rapid Spanning Tree Protocol (RSTP)

• The main difference between Rapid Spanning Tree Protocol (RSTP IEEE 802.1W) and Spanning Tree Protocol (STP IEEE 802.1D) is that Rapid Spanning Tree Protocol (RSTP IEEE 802.1W) assumes the three Spanning Tree Protocol (STP) ports states Listening, Blocking, and Disabled are same (these states  do not forward Ethernet frames and they do not learn MAC addresses). Hence Rapid Spanning Tree Protocol (RSTP IEEE 802.1W) places them all into a new called Discarding state. Learning and forwarding ports remain more or less the same.

• In Spanning Tree Protocol (STP IEEE 802.1D), bridges would only send out a BPDU when they received one on their Root Port. They only forward BPDUs that are generated by the Root Switch (Root Bridge). Rapid Spanning Tree Protocol (RSTP IEEE 802.1W) enabled switches send out BPDUs every hello time, containing current information.

•Spanning Tree Protocol (STP IEEE 802.1D) includes two port types; STP Root Port and Designated Port. Rapid Spanning Tree Protocol (RSTP IEEE 802.1W) includes two additional port types called as alternate ports and backup ports.

An alternate port is a port that has an alternative path or paths to the Root Switch (Root Bridge) but is currently in a discarding state (can be considered as an additional unused Root Port).  A backup port is a port on a network segment that could be used to reach the root switch, but there is already an active STP Designated Port for the segment (can be considered as an additional unused designated port).