FlexView Indirect Instancing

You can configure FlexViews to reference an instance from one MIB table to retrieve data from another MIB table. This feature allows the data returned in the referenced column to be used as the instance for the MIB object selected for this column. The referenced column must have been mapped to the Default request group. Indirect instancing uses the Instance Column (only available with Request Group 2, 3, or 4 selected) in the FlexView Properties window to specify the particular column that will be used. When indirect instancing is used in a FlexView, additional SNMP requests are assembled to retrieve the instanced data for the selected MIB object.

Request Groups are staged and queried in the following order: default, group 2, then group 3 and group 4 (group 3 and group 4 are sent to the device at the same time). Because of this order, a referenced column must be mapped to a lower group so that the referenced value is valid at the time of the query. For example, Request Group 2 can only reference the Default request group. Request Groups 3 and 4 can only reference values returned for Request Group 2 and the Default request group.

To see how this feature can be useful, consider the IETF dot1dBridge MIB. This MIB is instanced by dot1dBridgePortIndex. Unfortunately, the Bridge MIB doesn't contain any objects that describe each port in the bridge. A human readable description for each interface in a device can be found in the Interface Table, but this table is instanced by Interface Index (ifIndex) rather than dot1dBridgePortIndex. Because bridge ports and ifIndices are not mapped one-to-one, objects from the Bridge Table and Interface Table cannot be combined in a FlexView without indirect instancing.

For an example of how Indirect Instancing is used in an actual FlexView, see the “Bridge Port Summary” FlexView in the Bridge folder.

  NOTES:
  1. Console's FlexView logic doesn't assure that data that is obtained from one column and used as an instance in an SNMP GET for another column is a valid instance. There is no checking on the data type or the range of the data to assure that the resulting SNMP GET operation will be meaningful. You should carefully debug and test any custom FlexViews on a variety of devices before relying on the data returned in them.
  2. Request Group 4 cannot use a column in Request Group 3 for instancing. Group 3 and 4 requests are not staged; they are sent to the device at the same time.

Continuing with the example of the dot1dBridge MIB, it turns out that there is a relationship between dot1dBridgePorts and Interfaces. An object contained in the entry for each bridge port (in the Bridge MIB) called the dot1dIfIndex cross-references each bridge port with an entry in the Interface Table. Using indirect instancing, two new columns could be added to any Bridge MIB based FlexView that together allow a description of the interface mapped to each bridge port to be displayed.

The first column, containing the dot1dIfIndex object, would be associated with the default request block. A second column containing the IfDesc object would be assigned to request group 2 or 3 and would have the Instance Column setting reference the column containing the dot1difIndex.

When data for the new FlexView is retrieved from selected devices, a MIB walk using GETNEXT will first be done (on the bridge mib) to gather the data for all columns associated with the default request block. For each bridge port instance returned from each device, a PDU will be sent containing a GET request for the IFDesc object using the value returned for dot1dIfIndex as the instance for the GET operation. When the data is returned from the device, it will be inserted into the correct row/column of the FlexView. Once the FlexView is defined to your satisfaction, you may want to Hide the dot1dIfIndex column from the FlexView display and Save the FlexView.

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