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The sixth definition describes an

(mandatory). The sixth definition describes an ASN.1 type called


Rose & McCloghrie [Page 15]

RFC 1065 SMI August 1988

5. Extensions to the MIB

Every Internet-standard MIB document obsoletes all previous such

documents. The portion of a name, termed the tail, following the


{ mgmt version-number }

used to name objects shall remain unchanged between versions. New

versions may:

(1) declare old object types obsolete (if necessary), but not

delete their names;

(2) augment the definition of an object type corresponding to a

list by appending non-aggregate object types to the object types

in the list; or,

(3) define entirely new object types.

New versions may not:

(1) change the semantics of any previously defined object without

changing the name of that object.

These rules are important because they admit easier support for

multiple versions of the Internet-standard MIB. In particular, the

semantics associated with the tail of a name remain constant

throughout different versions of the MIB. Because multiple versions

of the MIB may thus coincide in "tail-space," implementations

supporting multiple versions of the MIB can be vastly simplified.

However, as a consequence, a management agent might return an

instance corresponding to a superset of the expected object type.

Following the principle of robustness, in this exceptional case, a

manager should ignore any additional information beyond the

definition of the expected object type. However, the robustness

principle requires that one exercise care with respect to control

actions: if an instance does not have the same syntax as its expected

object type, then those control actions must fail. In both the

monitoring and control cases, the name of an object returned by an

operation must be identical to the name requested by an operation.

Rose & McCloghrie [Page 16]

RFC 1065 SMI August 1988

6. Definitions



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