H3C Technologies H3C S7500E Series Switches - Manual (Page 136)

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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:
z 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.
z 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, alarm, event, history, and statistics, in most cases.
The H3C 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.
RMON Groups
Among the RMON groups defined by RMON specifications (RFC 2819), the realized public MIB
of the device supports the event group, alarm group, history group and statistics group. Besides,
H3C also defines and implements the private alarm group, which enhances the functions of the
alarm group. This section describes the five kinds of groups in general.
Ethernet statistics group
The statistics group defines that the system collects statistics on various traffic information on
an interface (at present, only Ethernet interfaces are supported) and saves the statistics in the
Ethernet statistics table (ethernetStatsTable) for query convenience of the management device.
It provides statistics about network collisions, CRC alignment errors, undersize/oversize
packets, broadcasts, multicasts, bytes received, packets received, and so on.
After the creation of a statistics entry on an interface, the statistics group starts to collect traffic
statistics on the interface. The result of the statistics is a cumulative sum.
History group
The history group defines that the system periodically collects statistics on traffic information at
an interface and saves the statistics in the history record table (ethernetHistoryTable) for query
convenience of the management device. The statistics data includes bandwidth utilization,
number of error packets, and total number of packets.
A history group collects statistics on packets received on the interface during each period,
which can be configured through the command line interface (CLI).