7.9. Mapping of the DEFVAL clause

The DEFVAL clause, which need not be present, defines an acceptable default value which may be used at the discretion of a SNMPv2 entity acting in an agent role when an object instance is created. During conceptual row creation, if an instance of a columnar object is not present as one of the operands in the correspondent management protocol set operation, then the value of the DEFVAL clause, if present, indicates an acceptable default value that a SNMPv2 entity acting in an agent role might use.

The value of the DEFVAL clause must, of course, correspond to the SYNTAX clause for the object. If the value is an OBJECT IDENTIFIER, then it must be expressed as a single ASN.1 identifier, and not as a collection of sub-identifiers.

Note that if an operand to the management protocol set operation is an instance of a read-only object, then the error `notWritable' [6] will be returned. As such, the DEFVAL clause can be used to provide an acceptable default value that a SNMPv2 entity acting in an agent role might use.

By way of example, consider the following possible DEFVAL clauses:

     ObjectSyntax       DEFVAL clause
     ----------------   ------------
     Integer32          DEFVAL { 1 }
                        -- same for Gauge32, TimeTicks, Unsigned32
     INTEGER            DEFVAL { valid } -- enumerated value
     OCTET STRING       DEFVAL { 'ffffffffffff'H }
     OBJECT IDENTIFIER  DEFVAL { sysDescr }
     BITS               DEFVAL { { primary, secondary } }
                        -- enumerated values that are set
     IpAddress          DEFVAL { 'c0210415'H } -- 192.33.4.21

Object types with SYNTAX of Counter32 and Counter64 may not have DEFVAL clauses, since they do not have defined initial values. However, it is recommended that they be initialized to zero.