Spanning Tree Protocol (STP)

Spanning Tree Protocol (STP) is a Layer 2 protocol that is used

It builds a logical loop free Layer 2 topology on a Layer 2 network that may have physical loops in its design. This is done by creating a tree structure, with a single switch as a root by strategically blocking specific ports on particular switches.

There are various versions of STP which include:

  • IEEE 802.1D the original STP standard
  • IEEE 802.1w Rapid Spanning Tree Protocol (RSTP)
  • IEEE 802.1s Multiple Spanning Tree Protocol (MST)
  • Per-VLAN Spanning Tree (PVST), a Cisco proprietary protocol used only for ISL VLAN encapsulation
  • Per-VLAN Spanning Tree Plus (PVST+), an improvement on the protocol supporting 802.1Q VLAN encapsulation.
  • Rapid Per-VLAN Spanning Tree Plus (Rapid PVST+), is a Cisco enhancement of RSTP. It provides a separate instance of RSTP 802.1w for each VLAN.


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