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SNMP Protocol Data Units

The Simple Network Management Protocol v2c (SNMPv2c) and v3 (SNMPv3) standards use protocol data units (PDUs) to contain messages between Network Management Systems (NMSs) and SNMP agents. The following table lists each available message type in the standard and a description.

Message	Description
GetRequest	An NMS sends a GetRequest message to an SNMP agent to request data from one or more variables on the target network device. The SNMP agent returns a Response message with the current data of the requested variables.
SetRequest	An NMS sends a SetRequest message to an SNMP agent to set values for one or more variables on the target network device. The SNMP agent returns a Response message with the current data of the requested variables for validation.
GetNextRequest	An NMS sends a GetNextRequest message to an SNMP agent to query for the next defined variable on the target network device. The SNMP agent returns a Response message with the next defined variable and its current value.
GetBulkRequest	An NMS sends a GetBulkRequest message to an SNMP agent to request data from multiple variables on the target network device. The SNMP agent returns a Response message with the current data of the requested variables. This optimized variation of the GetNextRequest message was introducted in SNMPv2.
Response	An SNMP agent sends a Response message to an NMS after being prompted by a request message from that NMS. The Response message normally contains variable bindings or errors
Trap	An SNMP agent sends an unsolicited Trap message to an NSM when an object defined in the MIB file on a host network device meets or exceeds a specific value.
InformRequest	The InformRequest message can be sent by either SNMP agents or NMSs. Since SNMP typically uses the UDP transport layer protocol, which does not use receipt confirmation messages, the InformRequest message was created to provide receipt confirmation, especially for Trap messages.