20.1.2 MIB Overview

A switch manages and provides SNMP managers with the following two types of MIBs: One is defined in an RFC, and the other is information prepared by the vendor who developed the switch.

MIB defined in RFC is called the normal MIB. Because standard MIBs are standardized, there are no differences in the information provided. MIB that the device developer prepares independently is called a private MIB, and the content varies depending on the device. Note, however, that MIB operations, including the retrieval and specification of information, are common to both standard and private MIBs. An operation specifies only the switch and the target MIB information. Specify the switch by using an IP address and specify the MIB information by using an object ID.

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(1) MIB architecture

Because a MIB has a tree structure, each node is identified by a number. Each item of MIB information is uniquely identified by assigning a sequential number to each node starting from the root. This sequential number is called the object ID and is assigned by adding, from the root, lower-level object group numbers by using dot notation. For example, the sysDescr MIB in the figure below is expressed by its object ID 1.3.6.1.2.1.1.1. The following figure shows an example of a MIB tree structure.

Figure 20-5 Example of the structure of the MIB tree

(2) How MIB objects are represented

An object ID consists of numbers in dot notation (for example, 1.3.6.1.2.1.1.1). Because a number-only ID is not easy to understand, some managers use mnemonics such as sysDescr for specification. If you specify a MIB by using a mnemonic, you must ascertain beforehand the MIB mnemonics the SNMP manager can use. To check the mnemonics that SNMP commands for the Switch can use, execute the snmp lookup command.

(3) Index

Although you use an object ID when you specify a MIB, some MIBs have only one meaning whereas other MIBs contain multiple items of information. You can identify a MIB by using an index. An index is expressed by adding a number after the object ID, and is used to indicate the number of the item of information.

When a MIB has only one meaning, add ".0" after the MIB object ID. If a MIB contains multiple information items, add a number indicating the number of the information items after the MIB object ID. For example, ifType (1.3.6.1.2.1.2.2.1.2) indicates the interface type. This switch has multiple interfaces. To check a specific interface type, you must specify the type specifically as type of the second interface. When specifying by MIB, the second indexing. 2 is appended to the end of MIB and referred to as ifType.2(1.3.6.1.2.1.2.2.1.2.2).

How an index is expressed depends on the MIB. A MIB entry expressed as INDEX {xxxxx,yyyyy,zzzzzz} in the MIB definition section of an RFC or other document has as its index xxxxx, yyyyy, and zzzzzz. Check the index for each MIB before performing MIB operations.

(4) Supported MIB of the Switch

The Switch provides the MIBs necessary for managing networks, such as those for switch status, interface statistics, and device information for the switch. Note that the definition file of private MIBs (ASN.1) is provided with the software.

For more information about MIB, see MIB Reference.