Contemporary-control-systems Compact Managed Switches Software Manual for Conso Uživatelský manuál stáhnout pdf (Strana 78)

TD020850-0MG

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

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Contemporary-control-systems Compact Managed Switches Software Manual for Conso Uživatelský manuál Strana 78