A method for authentication includes: a Gateway Mobile Station (G-MS) receives an authentication trigger message from a host, and sends the authentication trigger message to an authentication server through an Ethernet Convergence Sublayer (Eth-CS) to trigger authentication. A network system includes a G-MS, which is connected to a host and an authentication server in communicable mode. The G-MS is configured to: receive an authentication trigger message from the host and send the authentication trigger message to the authentication server through the Eth-CS. The authentication server is configured to: receive the authentication trigger message that the G-MS sends through the Eth-CS, and authenticate the host. A G-MS includes: a receiving unit, configured to receive an authentication trigger message from the host; and a sending unit, configured to send the authentication trigger message received by the receiving unit to the authentication server through the Eth-CS.