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:
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.
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:
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.
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.
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.
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.
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.
