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After the supported SNMP version is determined, the management station uses that
version to structure management data requests.
SNMP Components
Now, let's look at the different components of SNMP. As a network management
protocol, it defines the way network management information should be structured
and interpreted. The basis of this functionality is SNMP's MIB. A MIB is the rule base
for defining management data structures. The MIB is used by the management
station and agents to format management data requests. SNMP defines the
formatting of the management data structures in the Structure of Management
Information (SMI) definition. For SNMP v1, the SMI is described in RFC 1155. The
SMI for SNMP v2 is described in RFC 1902. Since SNMP is a hardware-independent
network manage ment protocol, it needs to accommodate the different data
representation generated by different types of devices. To facilitate this kind of
communication, SNMP uses Abstract Syntax Notation One (ASN.1). All network
management data structure requests and responses are formatted using ASN.1. In
order to transport these management messages, they must be encoded into a
format that will permit their transmission between managed devices and
management stations. SNMP defines this format as a set of data encoding rules
known as the Basic Encoding Rules (BER).
SMI
The SMIs for SNMP v1 and SNMP v2 define the hierarchical rules for describing
management data structures. The top of this structure is the MIB, which is
essentially a container for specific management data structures, known as managed
objects. Managed objects or MIB objects are the data mappings used by agents to
collect management data. A managed object exists for each management data
variable that is collected by the agent. Each object can contain a single data type
and value or a list of data types and values. The SNMP v1 and SMTPv2 SMIs define
two groups of data types: simple and application-wide. ASN.1 is used for the actual
representation and implementation of the SMI-defined data structures.
BER
The SNMP BER defines the process used to convert the ASN.1 format into a binary
format for transmission in the SNMP PDU. This serialized data is then converted
back into ASN.1 format when it reaches its destination. The actual SNMP-PDU data
is in BER hexadecimal form. The BER conversion is a function of the SNMP process
operating on the managed device. Only a subset of BER is used for SNMP; its usage
is a legacy of the CMIP standard, which uses the CCITT X.209 specification. From a