GeoDesy Pronto X Series User Manual
Page 49
GeoDesy Kft.
49
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PDU type -- Specifies the type of PDU being transmitted.
Request-ID -- Associates requests with responses.
Error-status -- Indicates an error and an error type. In SNMPv2 GetBulk operations,
this field becomes a NonRepeaters field. For these operations, this field defines the
number of request-ed variables listed that should be retrieved no more than once
from the beginning of the request. The field is used when some of the variables are
scalar objects with only one variable.
Error-index -- Associates the error with a particular object instance. In SNMPv2
GetBulk operations, this field becomes a Max Repetitions field. For these operations,
this field defines the maximum number of times that other variables beyond those
specified by the NonRepeaters field should be retrieved.
Variable-bindings -- Comprises the data of an SNMP PDU. Variable bindings
associate particular object instances with their current values.
Like SNMPv1 messages, SNMPv2 messages (shown in Figure 4) contain two parts.
The second part of the SNMPv2 message (the PDU) is virtually identical to that of an
SNMPv1 message (see the previous description of an SNMP PDU for differences).
The first part of the SNMPv2 message contains the majority of the differences
between SNMPv1 and SNMPv2.
Figure 4: SNMP v2 Message Format
The first part of a SNMPv2 message is often called a wrapper. The wrapper includes
authentication and privacy information in the form of destination and source parties.
As mentioned earlier, a party includes the specification of both an authentication and
a privacy protocol. In addition to a destination and a source party, the wrapper
includes a context. A context specifies the managed objects visible to an operation.
The authentication protocol is designed to reliably identify the integrity of the
originating SNMPv2 party. It consists of authentication information required to
support the authentication protocol used. The privacy protocol is designed to protect
information within the SNMPv2 message from disclosure. Only authenticated
messages can be protected from disclosure. In other words, authentication is
required for privacy.
The SNMPv2 specifications discuss two primary security protocols: one for
authentication and one for privacy. These are the Digest Authentication Protocol and
the Symmetric Privacy Protocol.