Management Information Base (MIB)

A MIB is nothing more than a database of objects. The MIB has a tree- like structure, similar to a file system. Each leaf object represents a parameter on the managed device. A common understanding of the MIB between NMS and agent is what allows SNMP communications to work.

For example, an NMS may need to query a router for interface errors on a particular interface. These requests do not take place in English, but by referencing a particular object identifier (OID) in the MIB for that device. The NMS may request the current value of object 1.3.6.1.2.1.2.2.1.20.0, which according to the MIB for that device is interface errors for a particular interface. When the NMS goes to ask a server about available disk space on a particular volume, it sends a different OID request to the server, which references an object in a MIB common to the NMS and the server.

OIDs are almost infinitely scaleable, and there are controls in place to make sure that OIDs from different vendors do not overlap. There are RFCs that define public MIBs, such as TCP/IP and Token Ring MIBs. There are also private MIBs, where vendors can create their own MIBs specific to their equipment and its functions.

MIBs can grow to tens of thousands of objects in size, and dealing with MIBs is a part of working with any NMS. Operators of the NMS frequently need to compile MIBs into the NMS. This allows outputs to have descriptive variable names rather than rather cryptic OIDs. Cisco maintains its private MIB definitions under the Cisco MIB subtree (1.3.6.1.4.1.9).