What is the default Forward Delay timer for STP?

The default Forward Delay timer for Spanning Tree Protocol (STP) is indeed 15 seconds. This timer is crucial for the process of transitioning ports between different states—specifically, from Listening to Learning, and then from Learning to Forwarding.

When a port is transitioning to the Forwarding state, the Forward Delay timer allows network topology to stabilize by introducing a delay. This is essential to prevent loops within the network, ensuring that all devices have synced their information about the network topology prior to beginning to forward frames. By using a default of 15 seconds, STP provides enough time for all devices in the network to receive and process the Bridge Protocol Data Units (BPDUs) they need for making informed decisions about which ports should be in forwarding or blocking states.

Changing this default value can significantly impact the convergence time of the network; thus, understanding its implications is important for network troubleshooting and design.