Understanding a MIB file
MIBs are text files that the creator of an SNMP agent provides to describe the variables the particular agent keeps track of. These variables are called SNMP objects.
 
Often, in the context of SNMP, they are simply referred to as objects.
MIBs have a very specific structure for the organization of objects; any SNMP management console (SNMP Management Console in this case) can use the MIB to form queries of the SNMP agent on a specific device. MIBs are supplied by the manufacturer of the device.
There are two logical sets of statistics that every agent (in theory) should keep track of:
The standard MIB-2 (RFC1213) set or MIB-1 (RFC1066), and
Any proprietary MIB(s) objects.
SNMP is structured this way so that each device can offer standard (MIB-1/2) data that would be common between all network devices (e.g., packets in, packets out), and data that is device-specific (like number of sheets printed on a network printer). MIB-2 is a superset of MIB-1. Sometimes these two sets of MIB objects are combined into one MIB file. Other times you may find that the manufacturer only provides you with a proprietary MIB and expects you to use the RFCMIB-2 (or MIB-1) to view the standard data objects. Unfortunately, there are manufacturers that only offer a subset of objects in the standard MIB(s). In these cases, you can ask the agent for the objects that are missing, but the agent will not respond.
All SNMP agents keep track of some or all of the objects in the standard MIBs (MIB-1 or MIB-2). If you do not have access to a proprietary MIB for your device, you may be able to get all the information you require from the standard MIBs.