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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