A method is provided for performing network selection and traffic routing. A user equipment (UE) receives an Access Network Discovery and Selection Function (ANDSF) rule including an Inter-System Routing Policy (ISRP) rule or an Inter-Access Point Name (Inter-APN) Routing Policy (IARP) rule. The UE receives, from a base station, radio access network (RAN) assistance information. The RAN assistance information received from the base station is used to evaluate the ISRP rule or the IARP rule of the ANDSF rule. The UE evaluates whether the ISRP rule or the IARP rule of the ANDSF rule is valid or not by using the RAN assistance information. The UE selects one of the RAN assistance information and the ANDSF rule including the ISRP rule or the IARP rule.