Simple Network Management Protocol (SNMP) is commonly used by management programs to monitor a variety of networked devices.
vSphere systems run SNMP agents, which can provide information to a management program in at least one of the following ways:
In response to a GET, GETBULK, or GETNEXT operation, which is a specific request for information from the management system.
By sending a notification which is an alert sent by the SNMP agent to notify the management system of a particular event or condition.
Management Information Base (MIB) files define the information that can be provided by managed devices. The MIB files define managed objects, described by object identifiers (OIDs) and variables arranged in a hierarchy.
vCenter Server and ESXi have SNMP agents. The agent provided with each product has different capabilities.