What is MIB?
A MIB (Management Information Base) is a standardized data
structure from various SNMP variables that are written in a
language independent from the target system.
Figure 1: Overview of MIB
With the manufacturer spanning standardization of MIBs and
access mechanisms, a heterogenous network with components made by
various manufacturers can be monitored and controlled. Today, the
following MIB standards are valid:
If component specific, non-standardized data is required for
network monitoring, they can be written into so-called private MIBs
by the manufacturers. Thus, also values that are not included in
the in the standard MIBs can be queried.
The information available for each private MIB can be obtained from
The RFC1213 determines the MIB II which is supported by all
SNMP-compliant devices. The RFC1213 is available for download
through this link:
The OSM/ESM with network management supports the following
- RFC1213: MIB II
- RFC 2233: Interface MIB
- RFC1286, RFC1493: Bridge–MIB
- RFC1757: RMON–MIB
The private MIB for SIMATIC NET network components is available
on the delivered CD. The private MIB file can also be loaded
directly with a Web browser via OSM/ESM.
http://<IP–adress of OSM/ESM>/snOSM.mib
A MIB describes the entirety of all SNMP objects (SNMP
variables) which are available in the network. The MIB information
is structured similar to the Windows registry.
The OID (Object Indentifier) describes the address of the MIB
object. For standardized MIB ojects, the address is fixed. Private
MIB objects are always stored in the "Enterprise" directory. The
addresses within this structure are set by the manufacturer. Only
the manufacturer number has to be registered. The following
internet page lists the registered manufacturers that provide
Figure 2: Structure overview
The standard object "sysdescr" (address of object
0.1.3.6.22.214.171.124.1) contains a description of SNMP components. For
the OSM TP62, the string "OSM TP62" is issued. To make private,
non-standardized information readable, these private MIBs have to
registered with a management station (e.g. SNMP OPC Server),
otherwise they cannot be addressed. To make MIB objects directly
readable and writable, so-called MIB browsers are used. MIB
browsers are often included in the standard delivery package of
network management applications.
To enable MIBs for integration in the system, so-called MIB
compilers have to be used. STEP 7 / NCM PC includes a MIB compiler
for configuring the SNMP/OPC server.
With the MIB Compiler from SIMATIC NET, any external device as well
as new SIMATIC NET devices can be linked.
However, this requires a MIB description for this device.
While the MIB administers various system aspects - like
information regarding nods or statistical information about the
throughput of packages, connections established, error messages
etc. - , the SMI represents the framework for the MIB which
describes exactly the kind of representation of objects and
exchange through the protocol with the help of "Structure of
Managed Information". Today, MIBs according to SMIv1 and SMIv2 are
available. For MIB Compilers for SIMATIC NET, those MIBs have to
conform to SMI v1. The SMI v2 format is not supported, but for most
SNMP components, both MIB formats are available.
MIB, SNMP, network management, OSM, ESM