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Object-Types: Data you can read and sometimes write
When reading the MIB, you'll also want to know what information you can directly request from the device, and what information you can send to the device. These functions are controlled by the SNMP commands GetRequest and SetRequest.
If you want to translate these commands into classic telemetry terms, you can roughly think of a GetRequest as an alarm poll and a SetRequest as a control command.
GetRequests and SetRequests operate on a type of element called an object-type. Object-types are called out in the MIB like this:
tmonAState OBJECT-TYPE
SYNTAX DisplayString (SIZE (8))
ACCESS read-only
STATUS mandatory
DESCRIPTION "The current alarm state."
::= {tmonAlarmEntry 4}
There are many different kinds of object-types. The specific object-types you might find in a MIB depend on the type of device, what kind of components it has, what the functions of those components, are, etc.
Quick Primer on SNMP MessagesIn SNMP v1, there are only 5 basic PDUs (program datagram units): GetRequest: a manager-to-agent message requesting the current value of a managed object. GetNext: a manager-to-agent message requesting the current value of the managed object one number after the one named in the request. (This is a way of walking down a table of values.) SetRequest: a manager-to-agent message that writes a new value to a managed object GetResponse: an agent-to-manager message in response to a GetRequest or a SetRequest. In either case, the message reports the current value of the managed object named in the manager's request Trap: an agent-to-manager message reporting a change in the value of a managed object |
You're probably not going to be interested in every object-type listed in the MIB, because you're not going to be interested in everything about the device's functions.
When searching for object-types, it's helpful to start with a plan of what functions of the device you want to manage. What information do you want to retrieve? What controls do you want to set? Knowing the device's functions and how you want to use them will help you narrow down what object-types you should look for in the MIB.
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