Address allocation method, device, and system

Embodiments of the present invention provide an address allocation method, device, and system. The method is applicable to a network with a broadband remote access server (BRAS), carrier grade network address translation (CGN) being set on the BRAS, and comprises: the BRAS detecting that a locally set CGN fails; the BRAS receiving an access request sent by a terminal; and the BRAS allocating a public network IP address to the terminal. According to the embodiments of the present invention, traffic transfer of the terminal needs not to be performed when the CGN fails, service restoration time of the terminal is shortened when the CGN of the BRAS fails, and the cost is reduced.