4.2.7. The InformRequest-PDU

An InformRequest-PDU is generated and transmitted at the request of an application in a SNMPv2 entity acting in a manager role, that wishes to notify another application (in a SNMPv2 entity also acting in a manager role) of information in a MIB view which is remote to the receiving application.

The destination(s) to which an InformRequest-PDU is sent is specified by the requesting application. The first two variable bindings in the variable binding list of an InformRequest-PDU are sysUpTime.0 [9] and snmpTrapOID.0 [9] respectively. If the OBJECTS clause is present in the invocation of the corresponding NOTIFICATION-TYPE macro, then each corresponding variable, as instantiated by this notification, is copied, in order, to the variable-bindings field.

Upon receipt of an InformRequest-PDU, the receiving SNMPv2 entity determines the size of a message encapsulating a Response-PDU with the same values in its request-id, error-status, error-index and variable-bindings fields as the received InformRequest-PDU. 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 InformRequest-PDU, and processing of the InformRequest-PDU terminates immediately thereafter. This alternate Response-PDU is formatted with the same values in its request-id field as the received InformRequest-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 InformRequest-PDU. Otherwise, the snmpSilentDrops [9] counter is incremented and the resultant message is discarded. Regardless, processing of the InformRequest-PDU terminates.

Otherwise, the receiving SNMPv2 entity:

1. presents its contents to the appropriate SNMPv2 application;

2. generates a Response-PDU with the same values in its request-id and variable-bindings fields as the received InformRequest-PDU, with the value of its error-status field is set to `noError' and the value of its error-index field is zero; and

3. transmits the generated Response-PDU to the originator of the InformRequest-PDU.