A tracing system is used to get the physical location of the target by IP address. The system combines Constraint-Based Geolocation with a landmark optimization algorithm, named Diversification Rectifies Advanced Greedy Overdetermined Optimization N-Dimension (DRAGOON), to estimate the geographic location of the target IP. The system selects a set of landmarks from the IP database. Then it uses direct contact between landmarks and targets IP by sending numerous Internet Control Message Protocol(ICMP) echo requests, recording the response time. Then the system measures the distance between landmarks and targets IP by delay time. Finally, the estimated location will be obtained by the delay-based measurement algorithm CBG.