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4.2.5. The SetRequest-PDU Connected: An Internet Encyclopedia
4.2.5. The SetRequest-PDU

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4.2.5. The SetRequest-PDU

4.2.5. The SetRequest-PDU

A SetRequest-PDU is generated and transmitted at the request of a SNMPv2 application.

Upon receipt of a SetRequest-PDU, the receiving SNMPv2 entity determines the size of a message encapsulating a Response-PDU having the same values in its request-id and variable-bindings fields as the received SetRequest-PDU, and the largest possible sizes of the error-status and error-index fields. If the determined message size is greater than either a local constraint or the maximum message size of the originator, then an alternate Response-PDU is generated, transmitted to the originator of the SetRequest-PDU, and processing of the SetRequest-PDU terminates immediately thereafter. This alternate Response-PDU is formatted with the same values in its request-id field as the received SetRequest-PDU, with the value of its error-status field set to `tooBig', the value of its error-index field set to zero, and an empty variable-bindings field. This alternate Response-PDU is then encapsulated into a message. If the size of the resultant message is less than or equal to both a local constraint and the maximum message size of the originator, it is transmitted to the originator of the SetRequest-PDU. Otherwise, the snmpSilentDrops [9] counter is incremented and the resultant message is discarded. Regardless, processing of the SetRequest-PDU terminates.

Otherwise, the receiving SNMPv2 entity processes each variable binding in the variable-binding list to produce a Response-PDU. All fields of the Response-PDU have the same values as the corresponding fields of the received request except as indicated below.

The variable bindings are conceptually processed as a two phase operation. In the first phase, each variable binding is validated; if all validations are successful, then each variable is altered in the second phase. Of course, implementors are at liberty to implement either the first, or second, or both, of these conceptual phases as multiple implementation phases. Indeed, such multiple implementation phases may be necessary in some cases to ensure consistency. The following validations are performed in the first phase on each variable binding until they are all successful, or until one fails:

  1. If the variable binding's name specifies an existing or non- existent variable to which this request is/would be denied access because it is/would not be in the appropriate MIB view, then the value of the Response-PDU's error-status field is set to `noAccess', and the value of its error-index field is set to the index of the failed variable binding.

  2. Otherwise, if there are no variables which share the same OBJECT IDENTIFIER prefix as the variable binding's name, and which are able to be created or modified no matter what new value is specified, then the value of the Response-PDU's error-status field is set to `notWritable', and the value of its error-index field is set to the index of the failed variable binding.

  3. Otherwise, if the variable binding's value field specifies, according to the ASN.1 language, a type which is inconsistent with that required for all variables which share the same OBJECT IDENTIFIER prefix as the variable binding's name, then the value of the Response-PDU's error-status field is set to `wrongType', and the value of its error-index field is set to the index of the failed variable binding.

  4. Otherwise, if the variable binding's value field specifies, according to the ASN.1 language, a length which is inconsistent with that required for all variables which share the same OBJECT IDENTIFIER prefix as the variable binding's name, then the value of the Response-PDU's error-status field is set to `wrongLength', and the value of its error-index field is set to the index of the failed variable binding.

  5. Otherwise, if the variable binding's value field contains an ASN.1 encoding which is inconsistent with that field's ASN.1 tag, then the value of the Response-PDU's error-status field is set to `wrongEncoding', and the value of its error-index field is set to the index of the failed variable binding. (Note that not all implementation strategies will generate this error.)

  6. Otherwise, if the variable binding's value field specifies a value which could under no circumstances be assigned to the variable, then the value of the Response-PDU's error-status field is set to `wrongValue', and the value of its error-index field is set to the index of the failed variable binding.

  7. Otherwise, if the variable binding's name specifies a variable which does not exist and could not ever be created (even though some variables sharing the same OBJECT IDENTIFIER prefix might under some circumstances be able to be created), then the value of the Response-PDU's error-status field is set to `noCreation', and the value of its error-index field is set to the index of the failed variable binding.

  8. Otherwise, if the variable binding's name specifies a variable which does not exist but can not be created under the present circumstances (even though it could be created under other circumstances), then the value of the Response-PDU's error-status field is set to `inconsistentName', and the value of its error- index field is set to the index of the failed variable binding.

  9. Otherwise, if the variable binding's name specifies a variable which exists but can not be modified no matter what new value is specified, then the value of the Response-PDU's error-status field is set to `notWritable', and the value of its error-index field is set to the index of the failed variable binding.

  10. Otherwise, if the variable binding's value field specifies a value that could under other circumstances be held by the variable, but is presently inconsistent or otherwise unable to be assigned to the variable, then the value of the Response-PDU's error-status field is set to `inconsistentValue', and the value of its error-index field is set to the index of the failed variable binding.

  11. When, during the above steps, the assignment of the value specified by the variable binding's value field to the specified variable requires the allocation of a resource which is presently unavailable, then the value of the Response-PDU's error-status field is set to `resourceUnavailable', and the value of its error- index field is set to the index of the failed variable binding.

  12. If the processing of the variable binding fails for a reason other than listed above, then the value of the Response-PDU's error- status field is set to `genErr', and the value of its error-index field is set to the index of the failed variable binding.

  13. Otherwise, the validation of the variable binding succeeds.

At the end of the first phase, if the validation of all variable bindings succeeded, then the value of the Response-PDU's error-status field is set to `noError' and the value of its error-index field is zero, and processing continues as follows.

For each variable binding in the request, the named variable is created if necessary, and the specified value is assigned to it. Each of these variable assignments occurs as if simultaneously with respect to all other assignments specified in the same request. However, if the same variable is named more than once in a single request, with different associated values, then the actual assignment made to that variable is implementation-specific.

If any of these assignments fail (even after all the previous validations), then all other assignments are undone, and the Response-PDU is modified to have the value of its error-status field set to `commitFailed', and the value of its error-index field set to the index of the failed variable binding.

If and only if it is not possible to undo all the assignments, then the Response-PDU is modified to have the value of its error-status field set to `undoFailed', and the value of its error-index field is set to zero. Note that implementations are strongly encouraged to take all possible measures to avoid use of either `commitFailed' or `undoFailed' - these two error-status codes are not to be taken as license to take the easy way out in an implementation.

Finally, the generated Response-PDU is encapsulated into a message, and transmitted to the originator of the SetRequest-PDU.


Next: 4.2.6. The SNMPv2-Trap-PDU

Connected: An Internet Encyclopedia
4.2.5. The SetRequest-PDU

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