The mixed denial-of-service attacks have become the mainstream threat to the Internet service availability.Tracing an individual attack packet to its origin is an important step in defending against such attacks.For this reason, researchers have proposed several approaches for single-packet IP traceback.However, these prior works suffer from the following disadvantages: The high process overhead at routers and low traceback accuracy.To address the issue, this paper proposes an efficient and precise approach, termed as S3T, for single-packet traceback based on label switching.Borrowing the idea of label switching principle in MPLS networks, its main method is to make use of the reverse routing to set up audit trails, and then employ parallel processing of audit trail establishment, more flexible storage assignment for traceback routers and adaptive adjustment for the audit trail retention time to overcome those drawbacks.Extensive analysis and simulation are carried out to conduct thorough numerical comparisons between S3T and the state-of-the-art approaches.The results show that S3T significantly outperforms the existing approaches in terms of the process overhead at routers, as well as the traceback accuracy.