Learn how to establish the Spanning Tree topology in a Layer 2 network using Bridge Protocol Data Units (BPDUs) to ensure a loop-free path and assign port roles.
STP uses a Spanning Tree algorithm to select one switch as the root of the Spanning Tree in a redundantly connected network. The algorithm calculates the best loop-free path through a switched Layer 2 network by assigning a role to each port based on its role in the active topology.
Procedure
| 1. | Power on all switches in the network. When switches are powered on, the Spanning Tree topology establishes itself in multiple stages. |
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| 2. | Allow each switch to function as the root switch and send configuration BPDUs through all ports. |
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| 3. | Enable switches to exchange BPDU information in order to compute the Spanning Tree topology. |
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| 4. | Review the information contained in each configuration BPDU.
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| 5. | When a switch receives a configuration BPDU with superior information (lower bridge ID, lower path cost), store the information for that port. |
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| 6. | If this BPDU is received on the root port of the switch, forward it with an updated message to all attached LANs for which it is the designated switch. |
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| 7. | If a switch receives a configuration BPDU with information less preferable than the information currently stored for that port, discard the BPDU. |
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| 8. | If the switch is a designated switch for the LAN from which the inferior BPDU was received, send that LAN a BPDU containing the up-to-date information stored for that port. |