Overview
A Management Information Base (MIB) is a hierarchical database that defines the variables (objects) that an SNMP manager can query or set on a managed device. Each object is identified by a unique Object Identifier (OID).
Structure
MIBs are structured like a tree. Standard MIBs (like MIB-II) define common objects like interface status and system uptime, while vendor-specific MIBs define objects unique to a particular manufacturer's hardware.
Importance
Without the correct MIB file, an SNMP manager might receive data from a device but won't know what that data represents (e.g., it sees a value of '2' but doesn't know it means 'Interface Down').