[SNMP4J] Basic Question about implementing SNMP Tables

[Frank Fock]

Hi,

First, you should use SMIv2 for new MIB modules.
Second, in SMIv2 all index columns must have
a maximum access of "not-accessible". Thus,
there will be no readable index-column - just
a virtual one.

Best regards,
Frank

inliner683 at gmx.de wrote:
> Hello,
> 
> I want to implement an agent serving a table defined in an own
> mib. The table rows will be created and deleted only by the agent
> itself dynamicalle to represent some information of a managed application.
> Cells in the table will be settable via a SNMP manager, but no row addition
> or removal should be possible via the manager.
> 
> I will explain my question on the following example. Having the MIB
> definition as follows:
> 
> SOMETABLE-MIB DEFINITIONS ::= BEGIN
> 
> IMPORTS
>        enterprises, OBJECT-TYPE, TimeTicks
>           FROM RFC1155-SMI
>        OBJECT-TYPE
>           FROM RFC-1212;
> 
> someCompany           OBJECT IDENTIFIER ::= { enterprises 1234 }
> someSubTree1          OBJECT IDENTIFIER ::= { someCompany 2 }
> someSubTree2          OBJECT IDENTIFIER ::= { someSubTree1 2 }
> 
> -- Some Table
> someTable     OBJECT-TYPE
>               SYNTAX SEQUENCE OF SomeEntry
>               ACCESS not-accessible
>               STATUS mandatory
>               DESCRIPTION ""
>               ::= { someSubTree2 1 }
> 
> someEntry     OBJECT-TYPE
>               SYNTAX SomeEntry
>               ACCESS not-accessible
>               STATUS mandatory
>               DESCRIPTION ""
>               INDEX { index }
>               ::= { someTable 1 }
> 
> SomeEntry     ::= SEQUENCE{
>                            index          INTEGER,
>                            someID             OCTET STRING,
>                            someVersion        OCTET STRING
>                           }
> 
> index         OBJECT-TYPE
>               SYNTAX INTEGER
>               ACCESS read-only
>               STATUS mandatory
>               DESCRIPTION "Row index."
>               ::= { someEntry 1 }
> 
> someID        OBJECT-TYPE
>               SYNTAX OCTET STRING (SIZE (0..30))
>               ACCESS read-write
>               STATUS mandatory
>               DESCRIPTION ""
>               ::= { someEntry 2 }
> 
> someVersion   OBJECT-TYPE
>               SYNTAX OCTET STRING (SIZE (0..30))
>               ACCESS read-write
>               STATUS mandatory
>               DESCRIPTION ""
>               ::= { someEntry 3 }      
>               
>     ::= { someSubTree2 2 }         
> END      
> 
> It' a simple table under the enterprises tree. The index column is the index of the table, the other
> columns are settable via SNMP. The table's SomeEntry is under the OID .1.3.6.1.4.1.1234.2.2.1.1.
> 
> 
> Now I have an implementation similar to the agenpro generator, first defining the OIDs:
> 
>     public static final OID oidSomeEntry = new OID(new int[]{1, 3, 6, 1, 4, 1, 1234, 2, 2, 1, 1});
>     public static final OID oidIndex = new OID(new int[]{1, 3, 6, 1, 4, 1, 1234, 2, 2, 1, 1, 1});
> 
>     public static final int colIndex = 1;
>     public static final int colSomeID = 2;
>     public static final int colSomeVersion = 3;
> 
>     public static final int idxIndex = 0;
>     public static final int idxSomeID = 1;
>     public static final int idxSomeVersion = 2;
> 
> The index definition is as follows:
> 
>         someEntryIndexes = new MOTableSubIndex[]{moFactory.createSubIndex(oidIndex,
>                 SMIConstants.SYNTAX_INTEGER, 1, 1)};
>         someEntryIndex = moFactory.createIndex(someEntryIndexes, false);
> 
> and the columns and table are created via:
> 
>         MOColumn[] someEntryColumns = new MOColumn[3];
>         someEntryColumns[idxIndex] = moFactory.createColumn(colIndex, SMIConstants.SYNTAX_INTEGER,
>                 moFactory.createAccess(MOAccessImpl.ACCESSIBLE_FOR_READ_ONLY));
>         someEntryColumns[idxSomeID] = new MOMutableColumn(colSomeID,
>                 SMIConstants.SYNTAX_OCTET_STRING, moFactory
>                         .createAccess(MOAccessImpl.ACCESSIBLE_FOR_READ_WRITE), null);
>         someEntryColumns[idxSomeVersion] = new MOMutableColumn(colSomeVersion,
>                 SMIConstants.SYNTAX_OCTET_STRING, moFactory
>                         .createAccess(MOAccessImpl.ACCESSIBLE_FOR_READ_WRITE), null);
> 
>         someEntryModel = moFactory.createTableModel(oidSomeEntry, someEntryIndex, someEntryColumns);
>         ((MOMutableTableModel) someEntryModel).setRowFactory(new SomeEntryRowFactory());
>         someEntry = moFactory.createTable(oidSomeEntry, someEntryIndex, someEntryColumns,
>                 someEntryModel);
> 
> This working fine so far and I want to add some rows to the table:
> 
> 
>         Variable v1[] = new Variable[3];
>         v1[0] = new Integer32(11);
>         v1[1] = new OctetString("someID1");
>         v1[2] = new OctetString("someVersion1");
>         Variable v2[] = new Variable[3];
>         v2[0] = new Integer32(22);
>         v2[1] = new OctetString("someID2");
>         v2[2] = new OctetString("someVersion2");
>         someEntry.addRow(new SomeEntryRow(new OID("1"), v1));
>         someEntry.addRow(new SomeEntryRow(new OID("2"), v2));
> 
> And this is the part which is confusing me. I would to expect to identify the table row via the index
> column and the base OID. So reading columns someID and someVersion in this example I would expect the OIDs
> 
> .1.3.6.1.4.1.1234.2.2.1.1.2.11
> .1.3.6.1.4.1.1234.2.2.1.1.3.11
> 
> to be valid. "11" is the value in the index column to identify the row. But using a mib browser these oids are invalid, and
> you must use the oids
> 
> .1.3.6.1.4.1.1234.2.2.1.1.2.1
> .1.3.6.1.4.1.1234.2.2.1.1.3.1
> 
> to get the values from 1st row. These are the OIDs used when creating the row. What is wrong here and why
> do I have to provide an (arbitrary?) OID when creating rows. I thought the OIDs should be deduced from
> the index column? This doesn't fit in my understanding of indexing tables in SNMP. Here you can provide
> arbitrary OIDs which will be valid and the index column seems to be of no importance.
> 
> As well I was wondering when the RowFactory will be used and by whom? Is this necessary when creating rows
> only by the agent itself?
> 
> Having answered these questions, I would like to be able to delete the table rows by the agent. What would be here the
> way to go?
> 
> Many thanks in advance.
> 
> 
> 
> 
> 
> 
> 

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