Next generation mobile communication systems will comprise both WLAN technologies and ad hoc networks. Ad hoc networks are formed by the spontaneous collaboration of wireless nodes. When communication to the Internet is desired, one or more nodes must act as gateways for the ad hoc network. In this case, global addressing of ad hoc nodes is required. In this paper, we present an IPv6 addressing architecture in order to be able to support ldquopurerdquo spontaneous IPv6 ad hoc networks but also to allow seamless integration between wireless LANs and ad hoc networks. It implies the possibility to discover a gateway/prefix pair which is used in order to build an IPv6 global address and, when necessary, to maintain a default route towards the Internet.