Understanding the network.pdf - Back to Home

accepted values are getRequest, getNextRequest, getResponse,
setRequest, and trap.
• PDU Length—Describes the size of the PDU (in octets) after the PDU length
field.
• Request ID—This field is used by the management station for matching send
requests with received requests. It is not used by the agent. However, the
agent needs to include the Request ID in its response to the management
station.
• Error Status—This field is used by the agent to notify the management
station that the request was a failure. Different values are supported to
indicate the type of error. If no error occurred, the field is set to zero.
• Error Index—This field (if possible) associates the error with a specific
variable binding that is contained in the PDU message body.
• Message Body—When management data is requested, it is done so using the
global OID of the management object. The agent in response sends the
value it has for the specified OID. This can be either an ASN.1 data type or a
NULL. It is also possible to specify the value of data type being requested.
These messages are known as variable bindings. Each variable binding
consists of four fields: length, OID, type, and value. When the variable
binding is sent as a request form to the management station, only the length
and OID fields will contain data. The amount of variable bindings contained
in a message is undefined. Instead, the size of the SNMP message is defined
by the agent and is typically 64 bytes in size. The message size is, however,
an adjustable variable.
• Enterprise—This field contains the variable-length OID of the object that has
generated the Trap message.
• Agent Address—This field contains the network address of the station that
has generated the Trap.
• Generic Trap Type—This field identifies the type of Trap message being sent
(linkup, linkDown, coldStart, warmStart, enterpriseSpecific, and
so on).
• Specific Trap Type—This field is used to indicate the type of Trap being
generated if it's not a generic Trap. If the generic Trap type is set to
enterpriseSpecific, this value is checked and compared to Traps listed in the
enterprise-specific MIB, which is indicated in the Enterprise Trap header
field.
• Time Stamp—This field indicates the time (in hundredths of a second) of the
Trap event relative to the system's bootstrap. It uses the MIB-2 sysUpTime
variable at the time of the Trap generation to derive this value.
• Message Body—This contains the variable bindings associated with the Trap
event.
• PDU Type—Specifically identifies this SNMP message as a GetBulkResponse
operation.