A method and a user equipment (UE) for routing a data packet in a wireless communication network are discussed. The method according to an embodiment includes establishing, by the UE, a packet data network (PDN) connection via a 3rd Generation Partnership Project (3GPP) cellular network; obtaining, by the UE from an Access Network Discovery and Selection Function (ANDSF) server, a routing rule including information on an access point name (APN) and a priority of the APN, the APN identifying a packet data network (PDN) connection; and performing, by the UE, an offload function by selecting a gateway via the 3GPP cellar network based on the priority of the APN. The routing rule comprises identification information in the form of an IP 5-tuple allowing the UE to route the data packet.