Chapter 65: RMON
988 Section X: Network Management
RMON Alarms
RMON alarms are used to generate alert messages when packet activity
on designated ports rises above or falls below specified threshold values.
The alert messages can take the form of messages that are entered in the
event log on the switch or traps that are send to SNMP programs.
The switch supports up to eight alarms. Each RMON alarm can monitor
one port and one RMON statistic.
RMON alarms consist of two thresholds. There is a rising threshold and a
falling threshold. The alarm is triggered if the value of the monitored
RMON statistic of the designated port exceeds the rising threshold. The
response of the switch is to enter a message in the event log, send an
SNMP trap, or both. The alarm is reset if the value of the monitored
statistic drops below the falling threshold.
The frequency with which the switch tests the thresholds in an alarm
against the actual RMON statistic is controlled by the time interval, a
setting you can adjust for each alarm.
Here are the three components that comprise RMON alarms:
RMON statistics group: A port must have an RMON statistics group if it
is to have an alarm. When you create an alarm, you specify the port to
which it is to be assigned not by the port number, but rather by the ID
number of the port’s statistics group. (As explained in “RMON Port
Statistics” on page 983, statistics groups are also used to remotely
view port statistics in the RMON portion of the MIB tree.)
RMON event: An event specifies the action of the switch when the
ingress packet activity on a port crosses a statistic threshold defined in
an alarm. The choices are to log a message in the event log of the
switch, send an SNMP trap to an SNMP workstation, or both. You can
create up to eight events. Since there are only three possible actions
and since events can be used with more than one alarm, you probably
will not create more than three events.
Alarm: The last component is the alarm itself. It defines the port
statistic to be monitored and the rising and falling thresholds that
trigger the switch to perform an event. The thresholds of an alarm can
have the same event or different events. The switch supports up to
eight alarms.
The following sections explain how to create and manage the various
elements of an alarm:
“Creating RMON Statistics Groups” next
“Creating RMON Events” on page 989
“Creating RMON Alarms” on page 990
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