A network device that translates addresses of machines on physically separate networks and filters packets at the link, network and transport layers implements a virtual LAN over interconnected computer networks transparent to the computer networks. Using authentication and encryption, a secure connection...http://www.google.com.hk/patents/US6047325?utm_source=gb-gplus-share專利 US6047325 - Network device for supporting construction of virtual local area networks on arbitrary local and wide area computer networks
