Detecting the occurrence of large-scale router failures and localizing the failed routers are critical to enhancing network reliability. We propose a two-phase approach for detecting and localizing large-scale router failures using traceroute-like active probes. To detect large-scale router failures, the detection phase is periodically invoked to probe all routers. When detecting large-scale router failures, the localization phase is triggered to identify the failed routers.We reduce the probing cost by avoiding three types of useless probes. For the routers whose status cannot be identified by probes, we develop a distance based method to estimate their failure probability. Experimental results based on ISP topologies show that the accuracy of our approach is higher than 96.5%, even when only 10% of routers are connected by end systems for probing. Compared with prior works, the proposed approach achieves much higher accuracy with lower probing cost.