nefu is a free application that monitors network services and reports outages. Working from a discription of the network topography, nefu\'s algorithm prevents \"false alarms\" in the event of a network outage due to a dependency failure. nefu is in production use at the University of Michigan, monitoring more than 250 servers (among which are U-M\'s IMAP, WWW, and LDAP Directory servers) and a variety of other systems.