A program or group of programs designed to provide an overall picture of the health of a given network. The two types of NMSes are active and passive. A passive NMS will generally live on a system that is designed to recieve SNMP traps and syslog messages from the various devices on the network, and will go into alert status on receipt of traps and/or syslog messages indicating a problem. An active NMS will poll the network using protocols such as ICMP, SNMP, and TCP to determine the status of a given list of hosts. The best NMSes, however, will combine both passive and active monitoring to provide a full, coherent picture of the network's health.