The University of Illinois at Urbana-Champaign (UIUC) has a large campus computer network serving a community of about 20,000 users. With such a large network, it is inevitable that there are a wide variety of technologies co-existing in a multi-vendor environment. Effective network monitoring tools can help monitor traffic and link usage, as well as detect faults and correct them before serious degradation or loss of service to the user community occurs. This report describes a network monitoring and fault detection tool that has been developed and is currently in operation at UIUC. This tool makes use of the Simple Network Management Protocol (SNMP) to collect data from the various network elements monitored and process the data into reports for the network administrator. The report contains discussions of internet subnetting, UIUCnet architecture, motivation and design considerations, data collection and processing, fault detection and isolation, and evaluation, together with comments. The appendices contain a description of the SNMP variables monitored, an SNMPLog, and examples of fault isolation. A glossary of terms and abbreviations is also provided. (52 references) (Author/DB)