Method and system for defending denial of service attack, wireless access point and wireless controller

The invention provides a method and a system for defending denial of service attack, a wireless access point and a wireless controller. The method comprises the following steps that: the wireless controller receives a first message of a client forwarded by the wireless access point; the wireless controller judges whether the first message is an attack message or not according to a receiving signal intensity indication threshold which corresponds to the client and is returned by the wireless access point; and the wireless controller directly discards the first message when determining that thefirst message is the attack message. By the method and the system for defending the denial of service attack, the wireless access point and the wireless controller which are provided by the invention, defense against a denial of service (DOS) attack can be realized, the client cannot be off-line or a wireless access service cannot be interrupted due to the DOS attack to the message, and the service quality of the wireless