The method comprises: reading a list item corresponding to the VLAN and having IP address not equal to the destination address from the users' information list on the layer-2 switch; the IP address ofsaid list item and MAC address is used as the source IP address and source MAC address to construct the ARP request message for the destination IP address; sending out said ARP request. By the invention, When intercepting users' information, the VLAN virtual interface and/or IP address has on needs to be specially configured in the VLAN without layer-3 forwarding function when sending ARP request.