Spanning Tree on DELL OS10 and Cisco Switches

Here’s the English translation, maintaining the HTML structure:

Spanning Tree is an algorithm that prevents packets from running in endless loops in a network by blocking connections that would cause such loops. Since Ethernet packets don’t have a maximum TTL (Time-To-Live), they could circulate indefinitely in the network without such a mechanism and impact performance.

On managed switches like those from DELL and Cisco, specific settings must be configured for Spanning Tree to work properly. Incorrect settings can result in one or multiple ports being completely blocked.

The Spanning Tree Protocol (STP) works by testing all paths through a network on a low-level basis for each port and determining where loops would form. The corresponding ports are then blocked accordingly to prevent this from happening. The network is continuously monitored, allowing STP rules to adapt based on the current situation.

Special attention should be paid to these factors:

• Spanning Tree Priority: Two switches must not have the same priority, otherwise nothing will work. Ensure that all switches have different priorities.
• Spanning Tree mode on ports: If these are not set correctly, no packets will be forwarded on the corresponding port. Ensure that VLANs and ports have the correct Spanning Tree modes (e.g., «edge»). Incorrect settings lead to ports that are UP and may even have working LACP, but cannot transmit a single IP packet.

Aktualisiert am 30. Juni 2025