Every SNMP agent has its own Management Information Base. The MIB defines variables whose values are set and updated by the agent. The MIB variables on the devices in the network enable the management software to monitor/control the network device. More formally, the MIB defines each variable as an object ID (OID). On most devices, the MIB then organizes the OIDs based in part on RFC standards, and in part with vendor proprietary variables. The MIB organizes all the variables into a hierarchy of OIDs, usually shown as a tree. Each node in the tree can be described based on the tree structure sequence, either by name or by number.
Working directly with an MIB, with long variable names and numbers, can be a bit of a challenge, so NMS software typically hides the complexity of the MIB variable numbering and names. However, to get a sense for the variable names, above example shows the tree structure for two variables, with the variable names being the long string of numbers shown at the bottom of the figure. Working with those numbers and the tree structure can be difficult at best. As a result, most people manage their networks using an NMS such as Cisco Prime. For perspective, you could use an SNMP manager and type MIB variable 1.3.6.1.4.1.9.2.1.58.0 and click a button to get that variable, to see the current CPU usage percentage from a Cisco router. However, most users of an NMS would much prefer to ignore those details and have a simple graphical interface to ask for the same information, never having to know that 1.3.6.1.4.9.2.1.58.0 represents the router CPU utilization MIB variable.
