04 - Le protocole STP [Français] - Les ports désignés et les ports non désignés

Introduction

This tutorial focuses on the Spanning Tree Protocol (STP), a crucial networking protocol that prevents loops in Ethernet networks. By understanding how designated and non-designated ports are chosen, you can effectively manage network redundancy and maintain a single active path between devices.

Step 1: Understanding the Purpose of STP

• STP is designed to prevent loops in network topologies.
• It operates at the data link layer of the OSI model, ensuring that there is only one active path between any two devices.
• By eliminating redundancy, STP improves network reliability and efficiency.

Step 2: Identifying Designated Ports

• Designated ports are the ports on a network switch that have the responsibility to forward traffic toward the root bridge.
• To identify designated ports, follow these criteria:
  • The port with the lowest cost path to the root bridge is selected as the designated port.
  • If there are multiple ports with the same cost, the port with the lowest port ID is chosen.
• Practical Tip: Regularly check the network configuration to ensure the correct designated ports are in place, especially after any changes to the network topology.

Step 3: Identifying Non-Designated Ports

• Non-designated ports are those that do not forward traffic toward the root bridge and are typically in a blocking state to prevent loops.
• Non-designated ports are determined based on:
  • The port cost relative to the designated port.
  • The overall topology of the network.
• Common Pitfall: Ensure that non-designated ports are configured correctly to avoid network disruptions. Misconfigured ports can lead to unexpected traffic behaviors.

Step 4: Monitoring STP Status

• Use network management tools or commands to monitor the status of STP on your switches.
• Commands may include:
  • show spanning-tree for Cisco devices to view the STP configuration and port status.
• Stay vigilant for changes in the network that may affect STP operations, such as new switches or changes in existing links.

Conclusion

Understanding how STP designates and non-designates ports is vital for maintaining a stable and efficient network. Regularly monitor your network's STP configuration and be proactive in managing port statuses to prevent loops and ensure optimal performance. For further learning, consider diving deeper into STP variations, such as Rapid STP or Multiple STP, to enhance your network's redundancy strategies.