Verifying whether the routing information originating from an AS is being correctly distributed throughout the Internet is important for stable inter-AS routing operation. However, the global behavior of routing information is difficult to understand because it changes spatially and temporally. Thus, rapid detection of inter-AS routing failures and diagnosis of their causes are also difficult. We have developed a multi-agent-based diagnostic system, ENCORE, to cope with these problems, and improved its functions (ENCORE-2) through our experience in applying the system to commercial ISPs. Cooperative actions among ENCORE-2 agents provide efficient methods for collecting, integrating, and analyzing routing information observed in multiple ASes to detect and diagnose anomalies that human operators have difficulty in handling. ENCORE-2 is also applied to the hijacked route problem, which is one of recent major inter-AS issues.