TCP/IP Structure of Management Information (SMI) and Management Information Bases (MIBs) Overview
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The Management Information Base (MIB) and MIB Objects
Given this backdrop, we can look at the SNMP Framework in a new light. The actual SNMP protocol itself, which we'll examine in the next section, has only a few, generic commands to accomplish read and write tasks as mentioned just above. It deals with only the methods by which network management information is exchanged between SNMP agents and SNMP network management stations. The network management information is really the heart of TCP/IP network management.
So, instead of SNMP being defined in terms of commands used to control particular devices, it is defined in terms of management information variables, generally called objects. Each object describes a particular characteristic of a device. Some objects are fairly generic and are meaningful for any device on a TCP/IP network; for example, an object describing something related to the Internet Protocol itself, such as the device's IP address. Other objects might be particular to a specific type of device; for example, a router will have objects that a regular host's Ethernet network interface card would not.
A collection of objects used in SNMP is called a management information base, or MIB. (In fact, SNMP objects are often called MIB objects.) The first version of SNMP, SNMPv1, had a single standard that defined the entire MIB for SNMP. Newer versions however provide more flexibility by using different MIB modules that defines sets of variables particular to the hardware or software used by a device.
Defining objects using modules allows for significant flexibility in defining the variables that allow management of different types of devices. A device can incorporate all the MIB modules appropriate to the hardware and software it uses. For example, if you had a device using Ethernet, it would incorporate variables from the Ethernet MIB; one using Token Ring would use the Token Ring MIB. Both devices would also use the common SNMP MIB that is used by all TCP/IP devices. Other modules might also be included as needed. We'll see more of how this works later in this section.
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