This invention relates to a method and a network device for establishing a Virtual Private Network (VPN) among Local Area Networks (LANs). The method uses a cloud controller that has a static IP address to control a plurality of network devices. The method comprises receiving, at the cloud controller, messages indicative of dynamic public network addresses associated with the first and second network devices; pre-assigning, at the cloud controller, the first and second network devices to an account maintained by the cloud controller; and sending an authorization message to the dynamic public network addresses associated with the first and second network devices to authorize the first and second network devices to establish a virtual network comprising two private networks to which the first and second network devices belong.