Which SNMP message is used to request a change to a variable?

The SetRequest message in the Simple Network Management Protocol (SNMP) is specifically designed for requesting a change to a variable within a managed device's information database. When a management application needs to alter the value of an SNMP-managed object, it utilizes the SetRequest message to send that update to the target device.

This message not only captures the object identifier (OID) of the variable intended for modification but also specifies the new value that should be assigned to that variable. This operation enables network administrators to configure various aspects of network devices programmatically.

In contrast, the other messages serve different purposes. For instance, the GetRequest is used to retrieve the current value of a variable without making any changes, while the GetNextRequest is utilized to traverse through a list of OIDs to fetch the next variable in a table. The Response message is sent by the managed device to the management application to report back the result of a GetRequest or the success/failure of a SetRequest. Hence, SetRequest is the correct choice for requesting a change to a variable.