gtpc1m2jTransmission Control Protocol/Internet Protocol

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.

Structure and Fields of SNMP PDUs

There are many types of structures and fields contained in the PDUs supported by the TPF system. Table 2 shows the format of the SNMP PDUs.

Table 2. GETREQUEST, GETNEXTREQUEST, SETREQUEST, GETRESPONSE PDU Format

Version Community name PDU type Request ID Error status Error index Variable binding list

Version
The version of the SNMP message. The TPF system supports version 1.

Community name
An ASCII display string of the name of the community from where the PDU originated. This value can be up to 255 characters in length.

PDU type
The type of PDU contained by the SNMP message. PDU type can be one of the following:

Request ID
A unique number that is used to distinguish between different requests and to associate them with the corresponding response.

Error status
Used to indicate that an error occurred while the agent was processing a request.

Error index
Used to provide additional information by identifying which variable in the list caused an error.

Variable binding list
A simple list of variable bindings, which are pairings of the names of MIB variables with their corresponding values.

Table 3 shows the format of the trap PDUs.

Table 3. Trap PDU Format

Version Community name PDU type Enterprise object identifier Network address Trap type Specific trap type Time stamp Variable binding list

PDU type
The type of PDU contained by the SNMP message; in this case, a trap PDU.

Enterprise object identifier
The unique identifier of the SNMP agent that is sending the trap. This value can be up to 255 characters in length.

Network address
The default IP address of the SNMP agent that is sending the trap.

Trap type
The type of trap PDU being sent. The following trap values can be defined:

For more information, see SNMP Traps.

Specific trap type
A user-defined value for an enterprise-specific trap.

Time stamp
The system up time, in hundredths of a second, for the system generating the trap.

All SNMP PDUs can contain a list of variable bindings. Table 4 shows the format of the variable binding.

Table 4. Variable Binding Format

Variable binding type: SEQUENCE_OF Length of the variable binding Type of object identifier Length of object identifier Value of object identifier Type of value for this object identifier Length of value for this MIB variable Value for this MIB variable