In general, an Internet gateway assigns an address to a node of an ad-hoc network on receipt of request for an address assignment. However, a load exerted to the Internet gateway increases. Accordingly, one (proxy node) of the nodes of an ad-hoc network can serve as a proxy node to perform an address assignment function of the Internet gateway. That is, if a node of the ad-hoc node does not receive an advertisement message, it requests the Internet gateway for address assignment to perform the proxy node function. The node is assigned with at least two addresses from the Internet gateway, and then assigns the address to the requesting node. Accordingly, a load exerted to the Internet gateway can be reduced.