The present invention discloses a method of dual stack access, wherein a network device authenticates the first protocol address of a requesting client, stores the user name, first protocol address, and address status information of the client in the user information table if the authentication succeeds, assigns a second protocol address to the client, stores this second protocol address and address status information in the user information table, generates control rules for the client according to its user information, and controls dual stack access of the client according to the rules. This invention provides effective authentication-based access control of dual stack users.