What is the purpose of MAC address filtering and how can attackers defeat it?

What will be an ideal response?

One of the most basic security mechanisms in wireless networks is MAC address filtering.  MAC addresses of legitimate stations are entered manually in the configuration interface of the AP's MAC address table, and only recognized stations can connect to the AP. However,
attackers get around this mechanism by sniffing the network to find legitimate MAC addresses, and then they alter frames by using those values. This tactic is called MAC address spoofing. The injected frame appears to be from a legitimate source, so attackers can connect to the AP and network.