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Cisco SRST SNMP MIB Release 3.4 Guide
OL-7959-01
Chapter 1 Cisco SRST SNMP MIB Support
Compliance
MIBs can be standard or enterprise. Internet standard MIBs are defined by working groups of the IETF
and published as RFCs. Enterprise MIBs are defined by other organizations, which are usually individual
companies. Done properly, enterprise MIBs instrument technology not covered by standard MIBs, either
completely or as an extension to a standard MIB.
The prototypical standard MIB is MIB-II, the second revision of the original SNMP MIB. MIB-II
contains branches for the basic areas of instrumentation, such as the system, its network interfaces, IP,
and TCP. All of these started out in a single MIB module, but as SNMPv2 evolves, they are being split
into separate modules.
Compliance
Cisco MIBs are a set of variables that are private extensions to the Internet standard MIB-II. The MIB-II
is documented in RFC 1213 (Management Information Base for Network Management of TCP/IP-based
Internets: MIB-II). This RFC includes information on the benefits of the new feature, supported
platforms, related documents, troubleshooting tips, configuration examples, and a detailed command
reference.
Cisco Compliance
At present, Cisco implementations of standard MIBs are often read-only or have some objects or object
groups missing because of security concerns or time requirements for implementation. Since
Cisco IOS Release 10.2, developers must document such specifics with AGENT-CAPABILITIES from
RFC 1904.
Implementation
To find what MIBs Cisco implements, start at ftp-eng.cisco.com with
ftp://ftp-eng.cisco.com/pub/mibs/README.
This contains a list of MIBs available for various software versions. The MIB list cannot account for
MIBs not included in a particular software subset or because a feature is turned off. Whether or not the
MIB is included is the function of AGENT-CAPABILITIES descriptions and the snmpORTable (RFC
1907) in later software versions.
SNMP MIB Tables
Tables are a powerful and often confusing aspect of SNMP MIBs. Architectural purists say SNMP has
conceptual tables, not real tables. This is because every object, whether in a table or not, is a leaf of the
tree, identified by an object identifier (OID) that includes an instance. So, in an abstract sense, all objects
are alike. But practically speaking, SNMP has tables, and using or implementing them gets somewhat
more complex than implementing scalars, which are single object instances.
Tables have a rigid structure, defined in the SMI. Tables can contain only simple objects, not other tables,
although multiple indexes can represent the concept of tables in tables. An entry, or row, in a table is
uniquely identified by one or more table indexes, also called auxiliary objects. The OID of an object from
a table is the OID for that object's position in the MIB tree concatenated with a representation of all the
table indexes for an entry in the table.
