A view subtree is the set of all MIB object instances which have a common ASN.1 OBJECT IDENTIFIER prefix to their names. A view subtree is identified by the OBJECT IDENTIFIER value which is the longest OBJECT IDENTIFIER prefix common to all (potential) MIB object instances in that subtree.
When the OBJECT IDENTIFIER prefix identifying a view subtree is longer than the OBJECT IDENTIFIER of an object type defined according to the SMI , then the use of such a view subtree for access control has granularity at the object instance level. Such granularity is considered beyond the scope of a SNMPv2 entity acting in an agent role. As such, no implementation of a SNMPv2 entity acting in an agent role is required to support values of viewSubtree  which have more sub-identifiers than is necessary to identify a particular leaf object type. However, access control information is also used in determining which SNMPv2 entities acting in a manager role should receive trap notifications (Section 4.2.6 of ). As such, agent implementors might wish to provide instance- level granularity in order to allow a management station to use fine-grain configuration of trap notifications.