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TCP/IP Remote Network Monitoring (RMON)
(Page 2 of 3)
RMON MIB Hierarchy and Object Groups
Since RMON is a MIB module, it consists
almost entirely of descriptions for MIB objects, with each having the
standard characteristics belonging to all such objects. All the objects
within RMON are arranged into the SNMP object name hierarchy within
the rmon group, which is group number 16 within the SNMP mib
(mib-2) object tree, 1.3.6.1.2.1. So, all RMON objects have identifiers
starting with 1.3.6.1.2.1.16. This single RMON group is broken down
into several lower-level groups that provide more structure for the
RMON objects defined by the specification. Figure 286
shows this structure.
Figure 286: SNMP Remote Network Monitoring (RMON) MIB Hierarchy RMON uses a special MIB module, rmon(16), which fits into the overall SNMP object hierarchy tree under mib/mib-2(1) within mgmt(2)just like other MIB object groups such as sys(1) and if(2); see Figure 273. Within this group, which has the group identifier 1.3.6.1.2.1.16, are 9 subgroups of RMON objects.
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Table 222
describes each of the RMON groups, showing for each its name, its group
code (which is used as the prefix for object
descriptors in the group), and its RMON
group number and SNMP object hierarchy identifier:
Table 222: SNMP RMON MIB Object Groups
RMON Group
Name
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RMON Group
Code
|
RMON Group
Number
|
Full Group
Identifier
|
Description
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statistics
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etherStats
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1
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1.3.6.1.2.1.16.1
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Objects that keep track of network
statistics measured by the device. Example statistics include network
traffic load, average packet size, number of broadcasts observed, counts
of errors that have occurred, the number of packets in various size
ranges and so forth.
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history
|
history,
etherHistory
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2
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1.3.6.1.2.1.16.2
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The history
group contains a single table object that controls how often statistical
data is sampled by the probe. The additional etherHistory group
is optional and contains extra Ethernet-specific information; it is
contained logically within the history group.
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alarm
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alarm
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3
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1.3.6.1.2.1.16.3
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This group defines the parameters
under which an alarm may be generated to inform an administrator of
an occurrence of import. The alarm group contains a table that
describes the thresholds that will cause an event to be triggered (see
the event group below).
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hosts
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host
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4
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1.3.6.1.2.1.16.4
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Contains objects
that keep track of information for each host on a network.
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hostsTopN
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hostTopN
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5
|
1.3.6.1.2.1.16.5
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This group contains objects that
facilitate reporting of hosts sorted in a particular way. The administrator
determines how these ordered statistics are tracked. For example, an
administrator could generate a report listing hosts sorted by the number
of packets transmitted, showing the most active devices.
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matrix
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matrix
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6
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1.3.6.1.2.1.16.6
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This group
keeps track of statistics for data exchanges between particular pairs
of hosts. So, the amount of data sent between any two devices on the
network could be tracked here. Since a large network could have thousands
of such device pairs, to conserve resources on the probe, often only
the most recent conversations between device pairs are kept
in the management information base.
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filter
|
filter
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7
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1.3.6.1.2.1.16.7
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This RMON group allows an administrator
to set up filters that control what sorts of network packets the probe
will capture.
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capture
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buffer,
capture
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8
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1.3.6.1.2.1.16.8
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This group
is used to allow a probe to capture packets based on particular parameters
set up in the filter group.
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event
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event
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9
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1.3.6.1.2.1.16.9
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When a particular alarm is triggered
based on the parameters in the objects in the alarm group, an
event is generated. This group controls how these events are processed,
including creating and sending an SNMP trap message to a network monitoring
station.
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The original RMON standard
was heavily oriented around Ethernet LANs, and you can see some of that
in the table above. Probes can also gather and report information related
to other networking technologies, by using other RMON groups created
for that purpose. The best example of this was the definition of a set
of groups specifically for Token Ring, which was defined in RFC 1513
in 1993.
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