History group
The history group defines that the system periodically collects statistics of traffic information on an
interface and saves the statistics in the history record table (ethernetHistoryTable) for query convenience
of the management switch. The statistics include 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 at the command line interface (CLI).
Event group
The event group defines event indexes. It controls the generation and notifications of the events triggered
by the alarms defined in the alarm group and the private alarm group. The events can be handled in one
of the following methods:
• Log—Logging event related information (the events that occurred, contents of the event, and so on)
in the event log table of the RMON MIB of the device. The management switch can check the logs
through the SNMP Get operation.
• Trap—Sending a trap to notify the occurrence of this event to the network management system
(NMS).
• Log-Trap—Logging event information in the event log table and sending a trap to the NMS.
• None—No action.
Alarm group
The RMON alarm group monitors alarm variables, such as the count of incoming packets (etherStatsPkts)
on an interface. After you define an alarm entry, the system gets the value of the monitored alarm
variable at the specified interval. When the value of the monitored variable is greater than or equal to
the rising threshold, a rising event is triggered. When the value of the monitored variable is smaller than
or equal to the falling threshold, a falling event is triggered. The event is then handled as defined in the
event group.
If an alarm entry crosses a threshold multiple times in succession, the RMON agent generates an alarm
event only for the first crossing. For example, if the value of a sampled alarm variable crosses the rising
threshold multiple times before it crosses the falling threshold, only the first crossing triggers a rising alarm
event, as shown in Figure 37.
Figure 37 Rising and falling alarm events
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