GETNEXT and SNMP Tables

I recently needed to understand actually how the ordering for the oids in an SNMP table need to be arranged for commands like snmpwalk and snmptable to correctly traverse a table.

So here is a MIB fragment for a table:

jmxTable OBJECT-TYPE
    SYNTAX      SEQUENCE OF jmxEntry
    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION
        ""
    ::= { monMIB 2 }
jmxEntry OBJECT-TYPE
    SYNTAX      JmxEntry
    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION
        ""
    INDEX       { routeIndex }
    ::= { jmxTable 1 }
JmxEntry ::= SEQUENCE {
    routeIndex    INTEGER,
    routeName     DisplayString,
    contextName     DisplayString,
    exchangesFailed INTEGER
}
routeIndex OBJECT-TYPE
    SYNTAX      INTEGER
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
        ""
routeName OBJECT-TYPE
    SYNTAX    DisplayString
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
        ""
    ::= { jmxEntry 2 }
contextName OBJECT-TYPE
    SYNTAX    DisplayString
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
        ""
    ::= { jmxEntry 3 }
exchangesFailed OBJECT-TYPE
    SYNTAX      INTEGER
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
        ""
    ::= { jmxEntry 4 }
We've got a four column table with a visible integer index, two text columns and a numeric column.

It turns out the important thing is that getnext on jmxEntry.0 must return jmxEntry.1.1.

Of course jmxEntry.0 doesn't exist in the MIB, except for its ability to respond to getnext.