Background: Know: alarm Recognize: etherStats

Anticipates: Event xxLM, traffic matrices, packet capture filters

Tag: Uncertain

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Alarming DiscussionEdit


Alarm group collects periodic samples from counters in the probe and compares them to user-defined thresholds. If a sample is collected and it exceeds the user-defined threshold, an event is generated. The specific action initiated by each event is defined in the Event Group. For example, a particular alarm will be created if more than 500 CRC errors detected in five minutes. The alarm group contains the only one table and each row of the table defines a particular alarm,containing the monitored variables, sampling intervals and thresholds etc..


An RMON alarm can monitor a specific MIB object such as etherStats, Host/matrix data and output of packet capture filtersby configuring the 'alarmVariable' value in alarm table.

Alarm SchemeEdit

An RMON alarm can also identify a specific eventTable entry to be triggered when a threshold is crossed.

Example of Alarm management in Dell Openmanage Switch Administrator

Example of alarm management in Dell Openmanage Switch Administrator


1. Two types of threshold:

a. Rising threshold
b. Falling threshold

2. Two types of values calculated for alarm:

a. Absolute Value
b. Delta Value

However, to prevent the duplicated alarms occured when the signal fluctuates near the threshold which increases the workload in the network, the engineering principle called Hysteresis is applied to the system.

Question: Does RMON2 extend alarms to cover OIDs outside RMON? No,because no OID is defined outside the RMON, so there is no alarm scheme used to protect even though RMON has this function.

Relationship with Event GroupEdit

Alarm group is used to monitor a particular object in MIB(Management Information Base). An alarm will be triggered When the value of this monitored object exceeds the upper limit or drops the lower limit. In this situation, alarm will be processed as an event. Recording in the log and sending SNMP trap are the two way to peocess the alarm. So alarm always triggers event. We need to make sure that the events(such as event-entry1) coresponding to the alarms or thresholds are defined and configurated in the table of Event Group. There is no alarm created even it satisfies the requirements of alarm if they don't exist in the event table. In conclusion, to realize the alarm group, we need to achieve the event group.

  • 1. For example, the alarmRisingEventIndex(9) and alarmFallingEventIndex(10) is the index of the eventEntry object that is used when a rising or falling threshold is crossed.

  • Here is another example in prectice, the Cisco RFGW-10 UEQAM software uses an event database to record the events in its system,and the stored events can be accessed using the show facility-alarm status command shown below to display the list of current active alarm and events on the Supervisor card[4]:
Router# show facility-alarm status [critical] [major] [minor] [info]

  • Cisco has Alarm and Event Dictionary[4] to describe the alarm and event notifications that the wireless LAN controller, access points, and location appliances can receive,like:



WCS Message

AP {0} on Switch {3} detected duplicate IP address {2} being used by machine with mac address {1}."


The system detects a duplicate IP address in the network that matches that assigned to an access point.

WCS Severity


Probable Causes

Another device in the network is configured with the same IP address as an access point.

Recommended Actions

Correct the misconfiguration of IP addresses in the network.

  • The table below also describes one alarm and event on Cisco ONS 15305 and 15302[5]:

Reference Number


Default Severity

Alarm Id (ProbCause)

Description (ProbCauseQ)

Detailed Description

Troubleshooting (or) Comments





Alarm condition on alarm-in port

The NEs provide four auxiliary alarm inputs (dry contact alarms) for associated equipment

See moreEdit

Control System Studio Guide For installers and maintainers of CSS Chapter 13 Alarm System


[1] How To Configure RMON Alarm and Event Settings Using SNMP Commands

[2] RFC2819 Remote Network Monitoring Management Information Base

[3] RFC2021Romote Network Monitoring Management Information Base Version2 using SMIv2 [4] Cisco Wireless Control System Configuration Guide, Release 4.1 [5] Common Alarms and Events Supported by ONS 15305 and ONS 15302