What is the correct function of the InformRequest message?

The InformRequest message is specifically designed to acknowledge a notification that has been received from a network device or management system. This message is part of the Simple Network Management Protocol (SNMP) framework, which is used for managing devices on IP networks.

When a device sends a notification—commonly termed a trap—the InformRequest serves as a response indicating that the notification was received. This functionality is essential in ensuring that the sender is aware that their message did not go unnoticed. In scenarios involving network monitoring and management, acknowledging notifications ensures reliable communication and allows for further action, if necessary, based on the received event.

The other options reference different functionalities that are not performed by the InformRequest. For instance, changing a variable’s value or requesting a variable's value involves different types of SNMP messages such as SetRequest or GetRequest. Discovering available variables would typically require a different mechanism involving SNMP's GetBulkRequest or similar approaches. Thus, the primary role of the InformRequest is to confirm receipt of notifications, making option B the correct function.