STP Flavors

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There are multiple versions of the Spanning Tree Protocol:

  • STP: The original specification of STP, defined in 802.1D. STP is sometimes referred to as Common Spanning Tree (CST) because it assumes one spanning tree instance for the entire switched network, regardless of the number of VLANs.
  • PVST+: Per-VLAN Spanning Tree Plus is a Cisco enhancement of STP that provides a separate 802.1D spanning tree instance for each VLAN configured in the network.
  • RSTP: Rapid STP, or IEEE 802.1w, is an evolution of STP that provides faster convergence than STP. However, RSTP still only provides for a single instance of STP.
  • Rapid PVST+: Cisco enhancement of RSTP that uses PVST+. Rapid PVST+ provides a separate instance of 802.1w per VLAN.
  • Multiple Spanning Tree Protocol: MSTP is an IEEE standard inspired by the earlier Cisco proprietary Multiple Instance STP (MISTP) implementation. MSTP maps multiple VLANs into the same spanning tree instance. The Cisco implementation of MSTP is MST, which provides up to 16 instances of RSTP and combines many VLANs with the same physical and logical topology into a common RSTP instance.

See: STP Varities

The charts below, taken from the excellent blog packetlife.net by Jeremy Stretch, summarize important information about STP. The first chart briefly introduces the key differences between each STP version.

The second chart illustrates the evolution of the STP standards.
See: Spanning tree cheat sheet version 2.0

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