Understanding the network.pdf - Back to Home

application-wide tags, which are used within an ASN.1 module;
context-specific tags, which are used to describe specific structured data
types; and private tags, which are used for special purpose data types. In
addition to the creation of classed data types, tagged data types also support
the use of specific semantics to defined specific data value ranges. This is
known as subtyping. To create the SMI-defined, SNMP-specific,
application-wide data types, ASN.1 application-class tags are used with
subtyping. These are defined in Table 11.5.
Table 11.5. SMI-Defined Application-Wide Data Types
Data Type Description
IpAddress ::=
[APPLICATION 0]
IMPLICT OCTET
STRING (SIZE(4))
Counter ::=
[APPLICATION 1]
IMPLICT INTEGER
(0..4294967295)
Gauge ::=
[APPLICATION 2]
IMPLICT INTEGER
(0..4294967295)
TimeTicks ::=
[APPLICATION 0]
IMPLICT INTEGER
(0..4294967295)
Opaque::=
[APPLICATION 0]
IMPLICT INTEGER
(0..4294967295)
Stores an IP address in four 8-bit octets.
An undefined variable counter that can store
increments up to 429,967,295. After it reaches the
maximum defined value, it returns to zero and
counts up again.
An undefined variable that can be any range between
0 and 429,967,295. The value can increase or
decrease between the set ranges. However, after the
minimum or maximum of the range is reached, the
value will remain at that value until the value shifts
toward the opposite range. Like a speedometer with
a range between 0 and 80, the car can be traveling at
90, but the speedometer reads 80.
A counter that increments in hundredths of a second
from a specified event. The counter maximum is 497
days, at which point the counter returns to 0.
This data type can be used to store data types that
are outside of the SMI definition. The data can be any
random information type that can be represented in
the integer range between -2,147,483,648 to
2,147,483,648.
• Structured—ASN.1 structured (or constructed) data types provide the
capability to represent a collection of one or more simple data types. There
are two ASN.1 structured data types used for this function: SEQUENCE and