SNMP MIB Terminology:

  MIB - A Management Information Base. It's a database, essentially, j
+ust not
        a familiar RDBMS. Every device that supports SNMP has one, whi
+ch you can
        query and update, if you know it's schema. The schema of a MIB
+ is 
        defined in a set of MIB files where each file contains modular
+ portions
        of the schema. Since each device may implement a different ove
+rall 
        schema, a module-based approach allows for that sort of flexib
+ility
        
        
  MIB File - An ASCII text file written according to the SMI format, w
+hich is 
             based on and defined using ASN.1. The MIB file is used to
+ define 
             and describe the schema of an SNMP MIB, or a portion of o
+ne.
             
             
  MIB Object - A queriable entity from an SNMP MIB. In a MIB browser, 
+this is 
               often described as a leaf or column. Each MIB Object is
+ defined 
               in a MIB file using the OBJECT-TYPE syntax. A MIB Objec
+t would
               define the following properties:

    object_type:    The name of this object in the SMI OBJECT-TYPE def
+inition 
                    in the MIB File.
    type_oid:       The OID of the object_type, as defined in the MIB.
    index_name[n]:  The name of the n-th index of this object-type, as
+ defined in
                    the MIB. (only valid for tables, table entries, an
+d columns)

                    
  Object Instance - To borrow terminology from Object Oriented Program
+ming, if a
                    MIB Object is a class definition, an Object Instan
+ce is an 
                    instance of an object of a class. In addition to t
+he 
                    properties of a MIB Object, it has the following w
+hich 
                    establish it's identity and value:

    value:         The actual value, as returned from a query to a dev
+ice.
    instance_id:   The specific identity of this object instance in a 
+device in
                   relation to it's object_type. It is a portion of an
+ OID 
                   string that is composed by the concatenation of one
+ or more 
                   indices.
    index_val[n]:  The value of the n-th index of this object's instan
+ce
    full_oid:      The full identifier for this particular object inst
+ance in a
                   device's MIB. It's the same as concatenating the ty
+pe_oid and 
                   instance_id
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Some additional notes:

An OID is a way of identifying objects in a MIB. an OID is composed of an array of Octets, represented by integers with a \. between each element. Each object in a MIB has a unique OID, and instances of objects have additional octets on the end that define their identity in relation to their object-type.

There are several types of objects, but only a few can be queried. The queriable object types are scalars and columns, but for the purposes of this we only will consider columns, because scalars are *much* simpler.

Column objects are assembled into groupings called Tables, and tables contain a Table Entry object which defines what indexes are used to construct the instance_id of available Object Instances of the column objects within the table.

These concepts are what SNMP is built on. SNMP is essentially object-oriented, but uses mechanisms and concepts that are (academically) supposed to be straight-forward to implement in C. (they usually aren't) It's both elegantly simple and frustratingly complex, depending on the implementation, much like some programming languages. ;)

Objects that I am presenting in these use cases will be specified not using their Numeric OIDs (.1.3.6.1.4.1...) but rather their Symbolic OIDs (textual names defined in the MIB Files)

First, a simple one:

ifTable.ifEntry.ifType
  - value is an integer representing the type of interface
  - index_val[0] is an integer value known as an ifIndex

ifTable.ifEntry.ifAdminStatus
  - value is an integer that represents an interface's administrative 
+state 
   (1=up,2=down,3=testing)
  - index_val[0] is an integer value known as an ifIndex
  
ifTable.ifEntry.ifInOctets
  - value is the number of bytes that have passed through the interfac
+e since
    being turned up.
  - index_val[0] is an integer value known as an ifIndex
[download]

We want to retrieve the full_oid of any ifInOctets objects whose instance_id matches (the instance_ids of all ifType objects whose value is 18) and (the instance_ids of all ifAdminStatus objects whose value is 1)


Second, a more complex one:

adMX2820M13PrvSlotTable.adMX2820M13PrvSlotEntry.adMX2820M13PrvCardPair
+ID
  - value is the name of the protection pair
  - index_val[0] is the slot number of this card in the pair
  
  
adGenPortSlotMapTable.adGenPortSlotMapEntry.adGenSlotAddress 
  - value is the slot number an interface is provisioned on
    (many interfaces per slot)
  - index_val[0] is the ifIndex value that corresponds to an interface
+ 
  
  
adMX2820M13StatDS3Table.adMX2820M13StatDS3Entry.adMX2820M13NetFuncServ
+State
  - value is a bitmask with the status of a DS3 circuit
  - index_val[0] is the ifIndex value that corresponds to this interfa
+ce
[download]

We want to retrieve the values of the adMX2820M13NetFuncServState objects that are only provisioned in slots whose adMX2820M13PrvCardPairID value is not blank and does not match '/not in use/i'