A network system comprising: a network device adapted to be coupled to a sender device for enabling data communication between said sender device and an outside target device, the network device being adapted for the outside target device to log onto the network device, said network device comprising: a proxy address resolution protocol, ARP, unit for comparing a target IP address contained in an ARP request frame broadcasted from said sender device with a first plurality of IP addresses in a proxy ARP table of said proxy ARP unit, and for generating an ARP reply frame containing a media access control, MAC, address of said network device according to a result of said comparison when said target IP address is matched with one IP address of said first plurality of IP addresses; a routing table for storing a second plurality of IP addresses for IP packet routing; and a processing unit coupled between said proxy ARP unit and said routing table, and for receiving said ARP request frame, and for assigning an IP address to said outside target device, and for updating said assigned IP address into said proxy ARP table and said routing table respectively, wherein said Proxy ARP unit is configured to not generate an ARP reply frame in a case where said target IP address is matched with an IP address of said second plurality of IP addresses but not matched with any IP address of said first plurality of IP addresses. a network device adapted to be coupled to a sender device for enabling data communication between said sender device and an outside target device, the network device being adapted for the outside target device to log onto the network device, said network device comprising: a proxy address resolution protocol, ARP, unit for comparing a target IP address contained in an ARP request frame broadcasted from said sender device with a first plurality of IP addresses in a proxy ARP table of said proxy ARP unit, and for generating an ARP reply frame containing a media access control, MAC, address of said network device according to a result of said comparison when said target IP address is matched with one IP address of said first plurality of IP addresses; a routing table for storing a second plurality of IP addresses for IP packet routing; and a processing unit coupled between said proxy ARP unit and said routing table, and for receiving said ARP request frame, and for assigning an IP address to said outside target device, and for updating said assigned IP address into said proxy ARP table and said routing table respectively, wherein said Proxy ARP unit is configured to not generate an ARP reply frame in a case where said target IP address is matched with an IP address of said second plurality of IP addresses but not matched with any IP address of said first plurality of IP addresses. a proxy address resolution protocol, ARP, unit for comparing a target IP address contained in an ARP request frame broadcasted from said sender device with a first plurality of IP addresses in a proxy ARP table of said proxy ARP unit, and for generating an ARP reply frame containing a media access control, MAC, address of said network device according to a result of said comparison when said target IP address is matched with one IP address of said first plurality of IP addresses; a routing table for storing a second plurality of IP addresses for IP packet routing; and a processing unit coupled between said proxy ARP unit and said routing table, and for receiving said ARP request frame, and for assigning an IP address to said outside target device, and for updating said assigned IP address into said proxy ARP table and said routing table respectively, wherein said Proxy ARP unit is configured to not generate an ARP reply frame in a case where said target IP address is matched with an IP address of said second plurality of IP addresses but not matched with any IP address of said first plurality of IP addresses.