Configuration restrictions and guidelines
When you set the spanning tree timers, follow these restrictions and guidelines:
The length of the forward delay is related to the network diameter of the switched network. The larger the network diameter is, the longer the forward delay time should be. As a best practice, use the automatically calculated value because inappropriate forward delay setting might cause temporary redundant paths or increase the network convergence time.
An appropriate hello time setting enables the device to promptly detect link failures on the network without using excessive network resources. If the hello time is too long, the device mistakes packet loss for a link failure and triggers a new spanning tree calculation process. If the hello time is too short, the device frequently sends the same configuration BPDUs, which wastes device and network resources. As a best practice, use the automatically calculated value.
If the max age timer is too short, the device frequently begins spanning tree calculations and might mistake network congestion as a link failure. If the max age timer is too long, the device might fail to promptly detect link failures and quickly launch spanning tree calculations, reducing the auto-sensing capability of the network. As a best practice, use the automatically calculated value.