Spanning Tree Protocol

Spanning Tree Protocol, or STP, allows switches to be aware of other switches through the sending and receiving of BPDUs (Bridge Protocol Data Units).

Spanning Tree Protocol can build a Layer 2 loop free topology by blocking traffic on redundant ports.

Spanning Tree Protocol operates by selecting a master switch and running an algorithm to identify which ports should and should not forward traffic.

Spanning Tree Protocol has multiple iterations:

  • Spanning Tree Protocol 802.1D – the original specification
  • Per-VLAN spanning tree, PVST
  • Per-VLAN spanning tree plus, PVST+
  • 802.1W Rapid Spanning Tree Protocol, RSTP
  • 802.1S Multiple Spanning Tree Protocol, MST

Cisco Catalyst switches can operate in three modes: PVST+, RSTP and MST. All three of these modes can work with the 802.1D through backwards compatibility.




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