Rmon; Rmon Overview; Working Mechanism - 3Com Baseline 2928 PWR Plus User Manual

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RMON

RMON Overview

Remote Monitoring (RMON) is used to realize the monitoring and management from the management
devices 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 traffic
information on the network segments connecting to its ports, such as total number of received packets
or total number of oversize packets received. The alarm function enables a managed device to monitor
the value of a specified MIB variable, log the event and send a trap to the management device when the
value reaches the threshold, such as the port rate reaches a certain value or the potion of broadcast
packets received in the total packets reaches a certain value.
Both the RMON protocol and the Simple Network Management Protocol (SNMP) are used for remote
network management:
RMON is implemented on the basis of the SNMP, which is thus enhanced. RMON sends traps to
the management device to notify the abnormality of the alarm variables by using the SNMP trap
packet sending mechanism. Although trap is also defined in SNMP, it is usually used to notify the
management device whether some functions on managed devices operate normally and the
change of physical status of interfaces. Traps in RMON and those in SNMP have different
monitored targets, triggering conditions, and report contents.
RMON provides an efficient means of monitoring subnets and allows SNMP to monitor remote
network devices in a more proactive and effective way. The RMON protocol defines that when an
alarm threshold is reached on a managed device, the managed device sends a trap to the
management device automatically, so the management device has no need to get the values of
MIB variables for multiple times and compare them, and thus greatly reducing the communication
traffic between the management device and the managed device. In this way, you can manage a
large scale of network easily and effectively.

Working Mechanism

RMON allows multiple monitors (management devices). A monitor provides two ways of data gathering:
Using RMON probes. Management devices can obtain management information from RMON
probes directly and control network resources. In this approach, management devices can obtain
all RMON MIB information.
Embedding RMON agents in network devices such as routers, switches, and hubs to provide the
RMON probe function. Management devices exchange data with RMON agents using basic SNMP
operations 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, and
event, in most cases.
The 3Com device adopts the second way and realizes the RMON agent function. With the RMON agent
function, the management device can monitor all the traffic flowing among the managed devices on all
connected LAN segments; obtain information about error statistics and performance statistics for
network management.
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