SNMP Interface Property Extender

The SNMP Interface property extender does much the same job as the Pointer-Like Index extender, but it is specialized for importing properties from the ifTable. Resources representing rows in the ifTable are modeled differently in Meridian compared to other tabular resource types, and this extender accounts for those differences.

This is helpful when the string property that you want to import is associated with a network interface, represented by a row in the ifTable. For example, the dot1dBasePortTable has its own index which does not share any components with any other table, but its dot1dBasePortIfIndex column contains a value that is a valid ifIndex.

   dot1dBasePortEntry OBJECT-TYPE
       -- ...
           "A list of information for each port of the bridge."
       -- ...
       INDEX  { dot1dBasePort } (1)
  -- ...

   dot1dBasePortIfIndex OBJECT-TYPE (2)
       -- ...
           "The value of the instance of the ifIndex object,
           defined in IF-MIB, for the interface corresponding
           to this port."
       ::= { dot1dBasePortEntry 2 }
  -- ...

    -- ...
            "An entry containing management information applicable to a
            particular interface."
    INDEX   { ifIndex } (3)
    ::= { ifTable 1 }
1 The entry type for dot1dBasePortTable is indexed on dot1dBasePort, which has no significance outside this table.
2 dot1dBasePortTable contains column dot1dBasePortIfIndex, which tells us the ifIndex corresponding to the physical port underlying the associated bridge base port.
3 ifIndex is the index of the ifTable entry type (and of the ifXTable entry type, as well).

By using this extender, it’s possible to import string attributes from the ifTable, ifXTable, or another table that augments the ifTable.


The SNMP Interface property extender expects two or three parameters:

Name Description Default Value



The alias name of the string property to import from the source MIB table.



The name of the column in the target MIB table that contains a value of ifIndex.




The name of the column in the source MIB table that contains a value of ifIndex.


The following example shows how to use dot1dBasePortIfIndex as a pointer-like index to import ifDescr from the ifTable, and ifName and ifAlias from the ifXTable, into a trio of new string properties in the target resource:

<resourceType name="dot1dBasePortEntry" label="dot1d Base Port" resourceLabel="${index}">
  <persistenceSelectorStrategy class="" />
  <storageStrategy class="" />

  <group name="ifTable" ifType="all">
    <mibObj oid="."     instance="ifIndex" alias="interfaceIndex" type="string" /> (1)
    <mibObj oid="."     instance="ifIndex" alias="interfaceDescr" type="string" />
    <mibObj oid="."  instance="ifIndex" alias="interfaceName"  type="string" />
    <mibObj oid="." instance="ifIndex" alias="interfaceAlias" type="string" />

  <group name="dot1dBasePortTable" ifType="all">
    <mibObj oid=" ." instance="dot1dBasePortEntry" alias="dot1dBasePort"        type="string" />
    <mibObj oid=" ." instance="dot1dBasePortEntry" alias="dot1dBasePortIfIndex" type="string" /> (2)
    <mibObj oid=" ." instance="dot1dBasePortEntry" alias="d1dBPDelayExDiscard"  type="counter" />
    <mibObj oid=" ." instance="dot1dBasePortEntry" alias="d1dBPMtuExDiscard"    type="counter" />
    <property instance="dot1dBasePortEntry" alias="dot1dBasePortIfDescr" class-name="org.opennms.netmgt.collectd.InterfaceSnmpPropertyExtender"> (3)
      <parameter key="source-ifindex-attribute" value="interfaceIndex"/>
      <parameter key="source-attribute" value="interfaceDescr"/> (4)
      <parameter key="target-ifindex-pointer-column" value="dot1dBasePortIfIndex"/>
    <property instance="dot1dBasePortEntry" alias="dot1dBasePortIfName" class-name="org.opennms.netmgt.collectd.InterfaceSnmpPropertyExtender"> (5)
      <parameter key="source-ifindex-attribute" value="interfaceIndex"/>
      <parameter key="source-attribute" value="interfaceName"/> (6)
      <parameter key="target-ifindex-pointer-column" value="dot1dBasePortIfIndex"/>
    <property instance="dot1dBasePortEntry" alias="dot1dBasePortIfAlias" class-name="org.opennms.netmgt.collectd.InterfaceSnmpPropertyExtender"> (7)
      <parameter key="source-ifindex-attribute" value="interfaceIndex"/>
      <parameter key="source-attribute" value="interfaceAlias"/> (8)
      <parameter key="target-ifindex-pointer-column" value="dot1dBasePortIfIndex"/>
1 Collect ifIndex, ifDescr, ifName, and ifAlias in a group associated with the ifIndex source resource-type, using modified names to avoid collisions with internal workings (the ifIndex type is built in, so we do not need a custom resource-type definition for it).
2 Collect the pointer-like column dot1dBasePortIfIndex in the target group.
3 To derive the dot1dBasePortIfDescr string property, tell the extender which target attribute contains the pointer-like value, which source column needs to have a matching value, and that we want to use the interfaceDescr property.
4 From the source group.
5 Deriving dot1dBasePortIfName is almost identical, except that we want the property interfaceName.
6 From the source group instead.
7 Again with dot1dBasePortIfAlias, we repeat ourselves except that our desired property from the source group is interfaceAlias
8 From the source group.