MAC Reduction Feature: Switch has to allocate a different MAC address for each VLAN on which spanning-tree is enabled. Sometimes the numbers of MAC Addresses are less than the number of VLANs available. To fix this, we use MAC address reduction feature. In this we add “System ID extension” in the Bridge ID. So, the new priority becomes Priority = System ID Extension (VLAN ID) + Priority. One important thing, the Bridge priority can be anywhere between 0 & 65535 with MAC reduction feature disabled. But when MAC reduction feature is enabled, the priority can only be a multiple of 4096.