📄 rfc1903.txt
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For example, ifIndex.3 would point to the 3rd row in the ifTable (note that if ifIndex were not-accessible, then ifDescr.3 would be used instead)." SYNTAX OBJECT IDENTIFIERRowStatus ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "The RowStatus textual convention is used to manage theSNMPv2 Working Group Standards Track [Page 6] RFC 1903 Textual Conventions for SNMPv2 January 1996 creation and deletion of conceptual rows, and is used as the value of the SYNTAX clause for the status column of a conceptual row (as described in Section 7.7.1 of [2].) The status column has six defined values: - `active', which indicates that the conceptual row is available for use by the managed device; - `notInService', which indicates that the conceptual row exists in the agent, but is unavailable for use by the managed device (see NOTE below); - `notReady', which indicates that the conceptual row exists in the agent, but is missing information necessary in order to be available for use by the managed device; - `createAndGo', which is supplied by a management station wishing to create a new instance of a conceptual row and to have its status automatically set to active, making it available for use by the managed device; - `createAndWait', which is supplied by a management station wishing to create a new instance of a conceptual row (but not make it available for use by the managed device); and, - `destroy', which is supplied by a management station wishing to delete all of the instances associated with an existing conceptual row. Whereas five of the six values (all except `notReady') may be specified in a management protocol set operation, only three values will be returned in response to a management protocol retrieval operation: `notReady', `notInService' or `active'. That is, when queried, an existing conceptual row has only three states: it is either available for use by the managed device (the status column has value `active'); it is not available for use by the managed device, though the agent has sufficient information to make it so (the status column has value `notInService'); or, it is not available for use by the managed device, and an attempt to make it so would fail because the agent has insufficient information (the state column has value `notReady').SNMPv2 Working Group Standards Track [Page 7] RFC 1903 Textual Conventions for SNMPv2 January 1996 NOTE WELL This textual convention may be used for a MIB table, irrespective of whether the values of that table's conceptual rows are able to be modified while it is active, or whether its conceptual rows must be taken out of service in order to be modified. That is, it is the responsibility of the DESCRIPTION clause of the status column to specify whether the status column must not be `active' in order for the value of some other column of the same conceptual row to be modified. If such a specification is made, affected columns may be changed by an SNMP set PDU if the RowStatus would not be equal to `active' either immediately before or after processing the PDU. In other words, if the PDU also contained a varbind that would change the RowStatus value, the column in question may be changed if the RowStatus was not equal to `active' as the PDU was received, or if the varbind sets the status to a value other than 'active'. Also note that whenever any elements of a row exist, the RowStatus column must also exist.SNMPv2 Working Group Standards Track [Page 8] RFC 1903 Textual Conventions for SNMPv2 January 1996 To summarize the effect of having a conceptual row with a status column having a SYNTAX clause value of RowStatus, consider the following state diagram: STATE +--------------+-----------+-------------+------------- | A | B | C | D | |status col.|status column| |status column | is | is |status column ACTION |does not exist| notReady | notInService| is active--------------+--------------+-----------+-------------+-------------set status |noError ->D|inconsist- |inconsistent-|inconsistent-column to | or | entValue| Value| ValuecreateAndGo |inconsistent- | | | | Value| | |--------------+--------------+-----------+-------------+-------------set status |noError see 1|inconsist- |inconsistent-|inconsistent-column to | or | entValue| Value| ValuecreateAndWait |wrongValue | | |--------------+--------------+-----------+-------------+-------------set status |inconsistent- |inconsist- |noError |noErrorcolumn to | Value| entValue| |active | | | | | | or | | | | | | | |see 2 ->D| ->D| ->D--------------+--------------+-----------+-------------+-------------set status |inconsistent- |inconsist- |noError |noError ->Ccolumn to | Value| entValue| |notInService | | | | | | or | | or | | | | | |see 3 ->C| ->C|wrongValue--------------+--------------+-----------+-------------+-------------set status |noError |noError |noError |noErrorcolumn to | | | |destroy | ->A| ->A| ->A| ->A--------------+--------------+-----------+-------------+-------------set any other |see 4 |noError |noError |see 5column to some| | | |value | | see 1| ->C| ->D--------------+--------------+-----------+-------------+------------- (1) goto B or C, depending on information available to the agent.SNMPv2 Working Group Standards Track [Page 9] RFC 1903 Textual Conventions for SNMPv2 January 1996 (2) if other variable bindings included in the same PDU, provide values for all columns which are missing but required, then return noError and goto D. (3) if other variable bindings included in the same PDU, provide values for all columns which are missing but required, then return noError and goto C. (4) at the discretion of the agent, the return value may be either: inconsistentName: because the agent does not choose to create such an instance when the corresponding RowStatus instance does not exist, or inconsistentValue: if the supplied value is inconsistent with the state of some other MIB object's value, or noError: because the agent chooses to create the instance. If noError is returned, then the instance of the status column must also be created, and the new state is B or C, depending on the information available to the agent. If inconsistentName or inconsistentValue is returned, the row remains in state A. (5) depending on the MIB definition for the column/table, either noError or inconsistentValue may be returned. NOTE: Other processing of the set request may result in a response other than noError being returned, e.g., wrongValue, noCreation, etc. Conceptual Row Creation There are four potential interactions when creating a conceptual row: selecting an instance-identifier which is not in use; creating the conceptual row; initializing any objects for which the agent does not supply a default; and, making the conceptual row available for use by the managed device.SNMPv2 Working Group Standards Track [Page 10] RFC 1903 Textual Conventions for SNMPv2 January 1996 Interaction 1: Selecting an Instance-Identifier The algorithm used to select an instance-identifier varies for each conceptual row. In some cases, the instance- identifier is semantically significant, e.g., the destination address of a route, and a management station selects the instance-identifier according to the semantics. In other cases, the instance-identifier is used solely to distinguish conceptual rows, and a management station without specific knowledge of the conceptual row might examine the instances present in order to determine an unused instance-identifier. (This approach may be used, but it is often highly sub-optimal; however, it is also a questionable practice for a naive management station to attempt conceptual row creation.) Alternately, the MIB module which defines the conceptual row might provide one or more objects which provide assistance in determining an unused instance-identifier. For example, if the conceptual row is indexed by an integer-value, then an object having an integer-valued SYNTAX clause might be defined for such a purpose, allowing a management station to issue a management protocol retrieval operation. In order to avoid unnecessary collisions between competing management stations, `adjacent' retrievals of this object should be different. Finally, the management station could select a pseudo-random number to use as the index. In the event that this index was already in use and an inconsistentValue was returned in response to the management protocol set operation, the management station should simply select a new pseudo-random number and retry the operation. A MIB designer should choose between the two latter algorithms based on the size of the table (and therefore the efficiency of each algorithm). For tables in which a large number of entries are expected, it is recommended that a MIB object be defined that returns an acceptable index for creation. For tables with small numbers of entries, it is recommended that the latter pseudo-random index mechanism be used.SNMPv2 Working Group Standards Track [Page 11] RFC 1903 Textual Conventions for SNMPv2 January 1996 Interaction 2: Creating the Conceptual Row Once an unused instance-identifier has been selected, the management station determines if it wishes to create and activate the conceptual row in one transaction or in a negotiated set of interactions. Interaction 2a: Creating and Activating the Conceptual Row The management station must first determine the column requirements, i.e., it must determine those columns for which it must or must not provide values. Depending on the complexity of the table and the management station's knowledge of the agent's capabilities, this determination can be made locally by the management station. Alternately, the management station issues a management protocol get operation to examine all columns in the conceptual row that it wishes to create. In response, for each column, there are three possible outcomes: - a value is returned, indicating that some other management station has already created this conceptual row. We return to interaction 1.⌨️ 快捷键说明
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