Contemporary Control Systems Compact Managed Switches Software Manual for Console Access - Manual (Page 78)

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5.1.6 Message Format for SNMP Operations
Five SNMP operations are used in SNMP version 1 : get, get-next, set, get-response, trap.
The first four commands are used to send and receive information for managed objects and use
the same message format. Trap uses a different format discussed in Section 5.1.6.2.
5.1.6.1 Format of Command Messages
Each command message contains a header and a protocol data unit (PDU).
5.1.6.1.1 Message Header
The fields in the message header contain :
Version — 0, indicating SNMP version 1.
Community string — the community string, which authorizes NMS access to the switch.
5.1.6.1.2 Message Protocol Data Unit (PDU)
SNMPv1 PDUs contain a specific command (get, set etc.) and operands that indicate the object
instances involved in the transaction.
The fields in the PDU contain
:
PDU type — indicates the command type : get(0xA0), get-next(0xA1), set(0xA3), get-response(0xA2)
Request ID — a 4-octet integer used to match response to queries
Error Status — a single octet integer containing a value of zero in a request and the following
error status in a response
noError (0): no problem
tooBig (1): the response to your request was too big to fit into one response.
noSuchName (2): an agent was asked to get or set an OID that it can’t find; i.e., the OID
doesn’t exist. It can be used for an unsupported object.
badValue (3): a read-write or write-only object was set to an inconsistent value.
readOnly (4): this error is generally not used.
genErr (5): none of the previous errors.
Error Index — a single octet integer that associates an error with a particular object identifier
(OID). Only the response operation sets this field. Other operations set this field to zero.
Variable binding — contains a sequence of OIDs and values
Figure 55 — Format of the Command Message for SNMP Version 1