Abstract: A brief survey on the state-of-the-art research ofdetermining geographic location of IP addresses is presented. Theproblem of determining the geographic location of routers in InternetService Provider (ISP) topology measurement is discussed when there isinadequate information such as domain names that could be used. Nineempirical inference rules are provided, and they are respectively (1)rule of mutual inference, (2) rule of locality, (3) rule of ping-pongassignment, (4) rule of bounding from both sides, (5) rule ofpreferential exit deny, (6) rule of unreachable/timeout, (7) rule ofrelay hop assignment, (8) rule of following majority, and (9) rule ofvalidity checking based on interface-finding. In totally 2,563discovered router interfaces of a national ISP topology, only 6.4% ofthem can be located by their corresponding domain names. In contrast,after exercising these nine empirical inference rules, 38% of themhave been located. Two methods have mainly been employed to evaluate theeffectiveness of these inference rules. One is to compare the measuredtopology graph with the graph published by the corresponding ISP. Theother is to contact the administrator of the corresponding ISP for theverification of IP address locations of some key routers. Theconformity between the locations inferred by the rules and thosedetermined by domain names as well as those determined by whoisinformation is also examined. Experimental results show that theseempirical inference rules play an important role in determining thegeographic location of routers in ISP topology measurement.