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4.2.3. The GetBulkRequest-PDU Connected: An Internet Encyclopedia
4.2.3. The GetBulkRequest-PDU

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4.2.3. The GetBulkRequest-PDU

4.2.3. The GetBulkRequest-PDU

A GetBulkRequest-PDU is generated and transmitted at the request of a SNMPv2 application. The purpose of the GetBulkRequest-PDU is to request the transfer of a potentially large amount of data, including, but not limited to, the efficient and rapid retrieval of large tables.

Upon receipt of a GetBulkRequest-PDU, the receiving SNMPv2 entity processes each variable binding in the variable-binding list to produce a Response-PDU with its request-id field having the same value as in the request. Processing begins by examining the values in the non-repeaters and max-repetitions fields. If the value in the non-repeaters field is less than zero, then the value of the field is set to zero. Similarly, if the value in the max-repetitions field is less than zero, then the value of the field is set to zero.

For the GetBulkRequest-PDU type, the successful processing of each variable binding in the request generates zero or more variable bindings in the Response-PDU. That is, the one-to-one mapping between the variable bindings of the GetRequest-PDU, GetNextRequest- PDU, and SetRequest-PDU types and the resultant Response-PDUs does not apply for the mapping between the variable bindings of a GetBulkRequest-PDU and the resultant Response-PDU.

The values of the non-repeaters and max-repetitions fields in the request specify the processing requested. One variable binding in the Response-PDU is requested for the first N variable bindings in the request and M variable bindings are requested for each of the R remaining variable bindings in the request. Consequently, the total number of requested variable bindings communicated by the request is given by N + (M * R), where N is the minimum of: a) the value of the non-repeaters field in the request, and b) the number of variable bindings in the request; M is the value of the max-repetitions field in the request; and R is the maximum of: a) number of variable bindings in the request - N, and b) zero.

The receiving SNMPv2 entity produces a Response-PDU with up to the total number of requested variable bindings communicated by the request. The request-id shall have the same value as the received GetBulkRequest-PDU.

If N is greater than zero, the first through the (N)-th variable bindings of the Response-PDU are each produced as follows:

  1. The variable is located which is in the lexicographically ordered list of the names of all variables which are accessible by this request and whose name is the first lexicographic successor of the variable binding's name in the incoming GetBulkRequest-PDU. The corresponding variable binding's name and value fields in the Response-PDU are set to the name and value of the located variable.

  2. If the requested variable binding's name does not lexicographically precede the name of any variable accessible by this request, i.e., there is no lexicographic successor, then the corresponding variable binding produced in the Response-PDU has its value field set to `endOfMibView', and its name field set to the variable binding's name in the request.

If M and R are non-zero, the (N + 1)-th and subsequent variable bindings of the Response-PDU are each produced in a similar manner. For each iteration i, such that i is greater than zero and less than or equal to M, and for each repeated variable, r, such that r is greater than zero and less than or equal to R, the (N + ( (i-1) * R ) + r)-th variable binding of the Response-PDU is produced as follows:

  1. The variable which is in the lexicographically ordered list of the names of all variables which are accessible by this request and whose name is the (i)-th lexicographic successor of the (N + r)-th variable binding's name in the incoming GetBulkRequest-PDU is located and the variable binding's name and value fields are set to the name and value of the located variable.

  2. If there is no (i)-th lexicographic successor, then the corresponding variable binding produced in the Response-PDU has its value field set to `endOfMibView', and its name field set to either the last lexicographic successor, or if there are no lexicographic successors, to the (N + r)-th variable binding's name in the request.

While the maximum number of variable bindings in the Response-PDU is bounded by N + (M * R), the response may be generated with a lesser number of variable bindings (possibly zero) for either of three reasons.

  1. If the size of the message encapsulating the Response-PDU containing the requested number of variable bindings would be greater than either a local constraint or the maximum message size of the originator, then the response is generated with a lesser number of variable bindings. This lesser number is the ordered set of variable bindings with some of the variable bindings at the end of the set removed, such that the size of the message encapsulating the Response-PDU is approximately equal to but no greater than either a local constraint or the maximum message size of the originator. Note that the number of variable bindings removed has no relationship to the values of N, M, or R.

  2. The response may also be generated with a lesser number of variable bindings if for some value of iteration i, such that i is greater than zero and less than or equal to M, that all of the generated variable bindings have the value field set to the `endOfMibView'. In this case, the variable bindings may be truncated after the (N + (i * R))-th variable binding.

  3. In the event that the processing of a request with many repetitions requires a significantly greater amount of processing time than a normal request, then an agent may terminate the request with less than the full number of repetitions, providing at least one repetition is completed.

If the processing of any variable binding fails for a reason other than listed above, then the Response-PDU is re-formatted with the same values in its request-id and variable-bindings fields as the received GetBulkRequest-PDU, with the value of its error-status field set to `genErr', and the value of its error-index field is set to the index of the variable binding in the original request which corresponds to the failed variable binding.

Otherwise, the value of the Response-PDU's error-status field is set to `noError', and the value of its error-index field to zero.

The generated Response-PDU (possibly with an empty variable-bindings field) 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 GetBulkRequest-PDU. Otherwise, the snmpSilentDrops [9] counter is incremented and the resultant message is discarded.


Next: 4.2.3.1. Another Example of Table Traversal

Connected: An Internet Encyclopedia
4.2.3. The GetBulkRequest-PDU

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