Extreme Networks EPICenter Guide Manual page 56

Getting Started with EPICenter
How RMON Events are Generated
When you configure an RMON threshold condition, you must specify not only the value of the
threshold, but also the startup alarm condition. The initial occurrence of an RMON alarm is determined
by the Startup Alarm condition specified when the alarm is defined.
It is important to understand that, except for the initial occurrence of the alarm, an RMON alarm event
will be generated only the when the sample value of the variable crosses one of the thresholds for the
first time after having crossed the other threshold.
The following diagram, shown in
Delta values, where the startup alarm condition is set to "Rising" or "RisingOrFalling."
RMON Alarm Event Generation
Figure 22: RMON Alarm event generation
Sampled
variable
value
Rising
threshold
Falling
threshold
= alarm event generated
Because the initial sample value of the variable is greater than the value of the Rising threshold, an
RMON rising threshold trap is generated. A second trap occurs at the next sample interval (point A)
because the sample variable value is now less than the Falling Threshold. At point B the value again
passes the Rising Threshold, and another trap event is generated. However, no trap occurs at point C,
even though the value of the variable again becomes greater than the Rising Threshold, because the
value has not yet become less than the Falling threshold. Another Rising threshold trap event cannot
occur until after a Falling threshold alarm has occurred, as happens at point D.
Note that in order to have any of these trap events cause an alarm in the EPICenter Alarm System, you
need to define an alarm that responds to a RMON Rising Threshold or RMON Falling Threshold event.
If you define an alarm based on the RMON Rising Threshold event, then EPICenter alarms will
●
occur at the initial sample, and at points B and E. Because the alarm is defined to respond to RMON
Rising Threshold events, the falling threshold trap events that occur at points A and D do not trigger
an EPICenter alarm.
If you also define an alarm based on an RMON Falling Threshold event, then EPICenter alarms
●
would also be generated at points A and D.
56
Figure 22, shows how alarms are generated for an RMON rule using
Initial
sample
value
B C
A
Time (sample intervals)
E
D
EPICenter Concepts and Solutions Guide
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