06-06-2016 09:25 AM
I asked one of our engineers about this one and here is his response:
The forward delay is the amount of time that the switchport will stay in the listening and learning phase. The protocol default is 15 seconds, but this can be altered by configuration at the root bridge. Since the forwarding delay is observed for two phases of STP calculation (both listening and learning states) its real impact on convergence time must be multiplied by two.
I hope this helps.