1-11 RMONRMON OverviewRemote Monitoring (RMON) is used to realize the monitoring and management from the managementdevices to the managed devices on the network by implementing such functions as statistics and alarm.The statistics function enables a managed device to periodically or continuously track various trafficinformation on the network segments connecting to its ports, such as total number of received packetsor total number of oversize packets received. The alarm function enables a managed device to monitorthe value of a specified MIB variable, log the event and send a trap to the management device when thevalue reaches the threshold, such as the port rate reaches a certain value or the potion of broadcastpackets received in the total packets reaches a certain value.Both the RMON protocol and the Simple Network Management Protocol (SNMP) are used for remotenetwork management:z RMON is implemented on the basis of the SNMP, which is thus enhanced. RMON sends traps tothe management device to notify the abnormality of the alarm variables by using the SNMP trappacket sending mechanism. Although trap is also defined in SNMP, it is usually used to notify themanagement device whether some functions on managed devices operate normally and thechange of physical status of interfaces. Traps in RMON and those in SNMP have differentmonitored targets, triggering conditions, and report contents.z RMON provides an efficient means of monitoring subnets and allows SNMP to monitor remotenetwork devices in a more proactive and effective way. The RMON protocol defines that when analarm threshold is reached on a managed device, the managed device sends a trap to themanagement device automatically, so the management device has no need to get the values ofMIB variables for multiple times and compare them, and thus greatly reducing the communicationtraffic between the management device and the managed device. In this way, you can manage alarge scale of network easily and effectively.Working MechanismRMON allows multiple monitors (management devices). A monitor provides two ways of data gathering:z Using RMON probes. Management devices can obtain management information from RMONprobes directly and control network resources. In this approach, management devices can obtainall RMON MIB information.z Embedding RMON agents in network devices such as routers, switches, and hubs to provide theRMON probe function. Management devices exchange data with RMON agents using basic SNMPoperations to gather network management information, which, due to system resources limitation,may not cover all MIB information but four groups of information, statistics, history, alarm, andevent, in most cases.The 3Com device adopts the second way and realizes the RMON agent function. With the RMON agentfunction, the management device can monitor all the traffic flowing among the managed devices on allconnected LAN segments; obtain information about error statistics and performance statistics fornetwork management.
