How are STP timers and state transitions affected when a topology change occurs in an STP environment?
A.
All ports will temporarily transition to the learning state for a period equal to the max age timer plus the forward delay interval.
B.
All ports will transition temporarily to the learning state for a period equal to the forward delay interval.
C.
The default aging time for MAC address entries will be reduced for a period of the max age timer plus the forward delay interval.
D.
The default hello time for configuration BPDUs will be reduced for the period of the max age timer.
The answer ‘C’ is not clear – it should read: The aging time for MAC address entries will be reduced to the Forward Delay interval.
The default aging time does not change, it is still 300 seconds.
Also aging time is not reduced to fwd delay + max age… just so happens that if a device is transmitting its mac can stay in the table a little longer (up to max age).
-more explanation below-
The root bridge sets the TCN flag in its Configuration BPDU, which is relayed to every other bridge in the network signaling the topology change and cause all other bridges to shorten their bridge table aging times from the default (300 seconds) to the Forward Delay value (default 15 seconds).
Any stations that are actively communicating during this time are kept in the bridge table. This condition lasts for the sum of the Forward Delay and the Max Age (default 15 + 20 seconds).