Understanding Spanning Tree Protocol: Preventing Layer 2 Loops

TLDRLearn about Spanning Tree Protocol (STP) and how it prevents Layer 2 loops in network topology. STP places redundant ports in a blocking state and creates a single path to each point in the network. The root bridge is elected based on the lowest bridge ID, and all ports on the root bridge are in a forwarding state. The bridge priority field includes the extended system ID, which is set to the VLAN ID in PVST. The bridge priority can only be changed in units of 4096. Once the topology has converged, only the root bridge sends BPDUs.

Key insights

:leftwards_arrow_with_hook:STP prevents Layer 2 loops by placing redundant ports in a blocking state.

:evergreen_tree:The root bridge is elected based on the lowest bridge ID.

:electric_plug:All ports on the root bridge are in a forwarding state.

:1234:The bridge priority field includes the extended system ID for VLAN-based STP (PVST).

:arrow_right_hook:The bridge priority can only be changed in units of 4096.

Q&A

What is the purpose of Spanning Tree Protocol?

—Spanning Tree Protocol prevents Layer 2 loops in network topology.

How is the root bridge elected in STP?

—The root bridge is elected based on the lowest bridge ID among the switches.

What is the role of the root bridge in STP?

—All ports on the root bridge are in a forwarding state, and it sends BPDUs to other switches.

What is the bridge priority field in STP?

—The bridge priority field includes the extended system ID, which is set to the VLAN ID in PVST.

Can the bridge priority be changed in STP?

—Yes, the bridge priority can be changed in units of 4096.

Timestamped Summary

00:02In this video, we learn about Spanning Tree Protocol (STP) and how it prevents Layer 2 loops in network topology.

12:47The root bridge is elected based on the lowest bridge ID among the switches, and all ports on the root bridge are in a forwarding state.

16:55The bridge priority field includes the extended system ID for VLAN-based STP (PVST) and can only be changed in units of 4096.

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