A method for assigning a global address to a node in an ad-hoc network is provided. A joining node to the ad-hoc network generates a local address using its MAC address. The joining node inquires of its one-hop nodes about whether they occupy a local address that is the same as the generated local address. When the joining node is informed that there are no nodes occupying the same local address, it generates a global address using the generated local address and a global prefix provided from neighbor nodes. The joining node inquires of an Internet gateway about whether the generated global address is currently used. When the joining node is informed that there are no nodes currently using the same global address, the joining node is assigned the generated global address. Further, the joining node and the Internet gateway communicate messages via a relay node using a tunneling.