Protocol data units (PDUs)

Each SNMP message contains a protocol data unit (PDU). These SNMP PDUs are used for communication between SNMP managers and SNMP agents. The SNMP Version 1 architecture defines the following types of PDUs that flow between SNMP managers and SNMP agents:
GETREQUEST PDU
Sent by the SNMP manager to retrieve one or more requested MIB variables specified in the PDU.
GETNEXTREQUEST PDU
Sent by the SNMP manager to retrieve the next MIB variable that is specified in the PDU. You can have multiple requests in the PDU. This PDU is primarily used by the SNMP manager to walk through the SNMP agent MIB.
SETREQUEST PDU
Sent by the SNMP manager to set one or more MIB variables specified in the PDU with the value specified in the PDU.
GETRESPONSE PDU
Sent by the SNMP agent in response to a GETREQUEST, GETNEXTREQUEST, or SETREQUEST PDU.
TRAP PDU
An unsolicited message sent by the SNMP agent to notify the SNMP manager about a significant event that occurred in the agent.