Aging

In addition to the MAC address and the associated port, a bridge also records the time that the device was learned. Aging of learned MAC addresses allows the bridge to adapt to moves, adds, and changes of devices to the network. After a device is learned, the bridge starts an aging timer. Each time the bridge forwards or filters a frame from a device, it restarts that device's timer. If the bridge doesn't hear from a device in a preset period of time, the aging timer expires and the bridge removes the device from its table.

Aging ensures that the bridge tracks only active systems, and ensures that the MAC address table does not consume too much system memory.