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TCP/IP MIB Object Descriptors and Identifiers and the Object Name Hierarchy and Name Notation
(Page 3 of 4)
Structure of the MIB Object Name Hierarchy
Let's explore how the MIB object
tree is structured, and more importantly, how SNMP MIB objects fit into
it (you may find referring to Figure 273
useful as you proceed here.) The trees root has no label, and
has three children:
- ccitt(0): For ITU
(formerly the CCITT) standards. (Also seen as itu(0)).
- iso(1): For ISO standards.
- joint-iso-ccitt(2): For joint standards.
(Also seen as joint-iso-itu(2)).
Following the iso(1) node,
we see the following at the next several levels:
- Within iso(1), the ISO has created a subtree
for use by other organizations, called org(3).
- Within org(3), there is a subtree for
the United States Department of Defense, which as you may recall was
the originator of the Internet: dod(6).
- Within dod(6), there is a subtree called
Everything we work with in SNMP is
under this one very specific subtree: 18.104.22.168, which if we used the
text labels would be iso.org.dod.internet. Within this part
of the name space, there are six subtrees below:
- directory(1): Reserved for future
use by ISO.
- mgmt(2): The primary subtree where
MIB objects are located. This is 22.214.171.124.2. It contains
a subtree called mib(1), which is 126.96.36.199.2.1. When MIB-II was
created, a subtree called mib-2(1) was created using the same
- experimental(3): Contains objects
used for standards under development. This is 188.8.131.52.3.
- private(4): Used for objects defined
by private companies. This node, 184.108.40.206.4, has a subtree called enterprise(1),
which is 220.127.116.11.4.1.
- security(5): Reserved for security
- snmpV2(6): Defines objects used
specifically for SNMP version 2.
Figure 273: Global Object Name Hierarchy and SNMP MIB Hierarchies
This diagram shows the object name hierarchy defined by ISO and CCITT (ITU) to allow all types of objects to be universally represented. The path within this larger tree to the tree branches relevant to SNMP can be found by following the colored boxes. The two subtrees used for SNMP are shown in light blue. Each contains its own substructure (some of which is illustrated by boxes in purple) defining thousands of different MIB objects. The branch on the left side is used for generic MIB objects and the one on the right for private ones. A separate hierarchy is also define for SNMP V2.
Phew. So, what's the bottom line
of all this? Well, basically all MIB module objects are named within
one of these two branches of the overall object tree:
- Regular MIB Objects: These are in the
mib(1) subtree under mgmt(2): 18.104.22.168.2.1.
- Private MIB Objects: These are in the
enterprise(1) subtree under private(4), which is 22.214.171.124.4.1.
For example, within enterprise(1) there is an entry cisco(9)
for Cisco Systems. So all Cisco-specific MIB objects start with 126.96.36.199.4.1.9.
Clear as mud, right? Why didn't they
just make a separate hierarchy where mib was at the top
instead of 6 levels deep? How dare you even suggest such a thing. Don't
you understand the importance of global standards? J
All facetiousness aside, this name
hierarchy is a bit cumbersome to deal with (okay, more than a bit) but
it does allow us to keep MIB objects organized in a sensible way. Within
the 188.8.131.52.2.1 subtree we find most of the regular MIB objects used
in SNMP. Each subtree within 184.108.40.206.2.1 corresponds to one of the regular
SNMP object groups or a particular MIB module.
Key Concept: All MIB objects have object identifiers that fit within two branches of the global object hierarchy. Regular MIB objects (which are not vendor-specific) fit in the mib(1) subtree under mgmt(2): 220.127.116.11.2.1. Private objects, which can be created by a hardware vendor to assist in managing that vendors products, are in the enterprise(1) subtree under private(4), which is 18.104.22.168.4.1
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