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Configuring RMON
RMON is used by management devices to monitor and manage the managed devices on the network by
implementing such functions as statistics collection and alarm generation. The statistics collection 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 SNMP are used for remote network management:
• RMON is implemented on the basis of the SNMP, and is an enhancement to SNMP. 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 usually notifies 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, 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 does not need to get the values of MIB variables
for multiple times and compare them, reducing the communication traffic between the management
device and the managed device. In this way, you can manage a large scale network easily and
effectively.
Working mechanism
RMON allows multiple monitors (management devices). A monitor provides the following methods for
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 by using basic
SNMP operations to gather network management information, which, due to system resources
limitation, only covers four groups of MIB information, alarm, event, history, and statistics, in most
cases.
The HP device adopts the second way and realizes the RMON agent function. With the RMON agent
function, the management device can obtain the traffic that flow among the managed devices on each
connected network segments; obtain information about error statistics and performance statistics for
network management.
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