GeoDesy Pronto X Series User Manual
Page 47
GeoDesy Kft.
47
E-mail: [email protected]
H-1116 Budapest, Kondorfa str. 6-8. Telefon: 06-1-481-2050
Fax.: 06-1-481-2049
an interface is an example of a counter. In SNMPv1, counter size was not specified.
In SNMPv2, 32-bit and 64-bit counters are defined.
Gauges -- Non-negative integers that can increase or decrease, but latch at a
maximum value. The length of an output packet queue (in packets) is an example of
a gauge.
Time ticks -- Hundredths of a second since an event. The time since an interface
entered its current state is an example of a tick.
Opaque -- Represents an arbitrary encoding. This data type is used to pass arbitrary
information strings that do not conform to the strict data typing used by the SMI.
Integer -- Represents signed, integer-valued information. This data type redefines
the ASN.1 "integer" simple data type, which has arbitrary precision in ASN.1 but
bounded precision in the SMI.
Unsigned integer -- Represents unsigned integer-valued information. It is useful
when values are always non-negative. This data type redefines the ASN.1 "integer"
simple data type, which has arbitrary precision in ASN.1 but bounded precision in
the SMI.
Simply constructed types include two ASN.1 types that define multiple objects in
tables and lists:
Row -- References a row in a table. Each element of the row can be a simple type or
an application-wide type.
Table -- References a table of zero or more rows. Each row has the same number of
columns.
ISO document 8825 (Specification of Basic Encoding Rules for ASN.1) defines ISO's
BERs. The BERs allow dissimilar machines to exchange management information
by specifying both the position of each bit within the transmitted octets and the
structure of the bits. Bit structure is conveyed by describing the data type, length,
and value.
The SMI for SNMPv2 includes two documents: RFCs 1443 and 1444. RFC 1443
(Textual Conventions) defines the data types used within the MIB modules, while
RFC 1444 (Conformance Statements) provides an implementation baseline. The
SNMPv2 SMI also defines two new branches of the Internet MIB tree: security
(1.3.6.1.5) and SNMPv2 (1.3.6.1.6).
SNMP Operations
SNMP itself is a simple request/response protocol. NMSs can send multiple
requests without receiving a response. Six SNMP operations are defined:
Get -- Allows the NMS to retrieve an object instance from the agent.
GetNext -- Allows the NMS to retrieve the next object instance from a table or list
within an agent. In SNMPv1, when an NMS wants to retrieve all elements of a table