OpenNMS: Monitoring large systems and networks
Big Time
If you need to monitor very large networks, you need powerful software. OpenNMS offers serious monitoring capabilities in a truly open source package.
Despite administrators’ best efforts, networks, servers, and services are destined to fail at some point. Sometimes the failure is obvious (a fan goes out or a backhoe meets your network cable), and sometimes the failure is subtle (a DNS change that breaks email to a server).