After dynamic ARP inspection (DAI) is enabled, an AP detects the ARP request and reply packets transmitted on the VAPs, discards invalid and attack ARP packets, and sends an alarm to the connected AC. DAI prevents unauthorized users from connecting to external networks through the AP and protects authorized users from interference and ARP spoofing attacks. In addition, DAI protects the AP's CPU from ARP attacks, which, if not prevented, will cause unavailability of some functions on the AP or even make the AP break down.