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Application-wide data types—Including these seven types:
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Network addresses—Represent addresses from a protocol family. SNMPv1 supports only
32-bit IP addresses.
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Counters—Nonnegative integers that increase until they reach a maximum value; then, the
integers return to zero. In SNMPv1, a 32-bit counter size is specified.
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Gauges—Nonnegative integers that can increase or decrease but retain the maximum value
reached.
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Time ticks—A hundredth of a second since some event.
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Opaques—An arbitrary encoding that is used to pass arbitrary information strings that do not
conform to the strict data typing used by the SMI.
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Integers—Signed integer-valued information. This data type redefines the integer data type,
which has arbitrary precision in ASN.1 but bounded precision in the SMI.
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Unsigned integers—Unsigned integer-valued information that is useful when values are always
nonnegative. This data type redefines the integer data type, which has arbitrary precision in
ASN.1 but bounded precision in the SMI.
The SNMPv1 SMI defines structured tables that are used to group the instances of a tabular object (an
object that contains multiple variables). Tables contain zero or more rows that are indexed to allow
SNMP to retrieve or alter an entire row with a single Get, GetNext, or Set command.
SNMP is a simple request-response protocol. The NMS issues a request, and managed devices return
responses. This behavior is implemented by using one of four protocol operations:
Get—Used by the NMS to retrieve the value of one or more object instances from an agent. If the
agent responding to the Get operation cannot provide values for all the object instances in a list, the
agent does not provide any values.
GetNext—Used by the NMS to retrieve the value of the next object instance in a table or list within
an agent.
Set—Used by the NMS to set the values of object instances within an agent.
Trap—Used by agents to asynchronously inform the NMS of a significant event.
SNMPv2 is an improved version of SNMPv1. Originally, SNMPv2 was published as a set of proposed
Internet standards in 1993; currently, it is a Draft Standard. As with SNMPv1, SNMPv2 functions
within the specifications of the SMI. SNMPv2 offers many improvements to SNMPv1, including
additional protocol operations.
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