(Remote MONitoring) Enhancements to the management information base (MIB) structure used by the simple network management protocol (SNMP). In 1991, RMON added comprehensive network monitoring capabilities. In the standard MIB, the network device had to be queried to obtain information. RMON is proactive and can set alarms on a variety of traffic conditions, including specific types of errors. RMON works at layers 1 and 2 of the OSI model, but RMON2, standardized in 1995, added a parallel set of MIBs that allow inspection of network layer 3 and higher layers. RMON2 can specify which protocols and application traffic are monitored. The full RMON capabilities are very comprehensive, and only a subset is often placed in routers and other network devices. SMON for Switched Networks In 1999, SMON (switch monitoring) extended the MIB for switched networks, allowing switching equipment to be managed and monitored more thoroughly. For example, SMON supports virtual LANs (VLANs) and port mirroring, which copies one or more switch ports to another port for monitoring. See SNMP, MIB, RMON probe, VLAN and port mirroring.