Embodiments of the present invention disclose a data transmission method and system, and related apparatuses. In the embodiments of the present invention, a first network device receives an authentication request message of a to-be-processed user that is sent by a second network device; and the first network device determines attribute information of the to-be-processed user, and determines, when it is determined that the attribute information is tag attribute information, that the to-be-processed user is an attacked user, and then sends an access parameter message to the second network device, so that data of the to-be-processed user is transmitted through a connection built between the second network device and a third network device, therefore, the second network device can perform traffic isolation and traffic traction on the to-be-processed user, the impact of network attack is minimized, and normal running security of the network is improved.