SNMP MIB Data Access

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.

Access

The most important entry in an object-type description is the ACCESS line. This controls whether you can read and write the data described in the object-type.

There are three access settings: not-accessible, read-only and read-write.

Not-accessible means the object-type is there, but you can't request the data in a GetRequest.

Read-only means you can request the data in a GetRequest, but you can't write new data for the object-type in a SetRequest.

Read-write means you're free to retrieve the data in a GetRequest and write new data for the object-type in a SetRequest.

In the example of the alarm state object-type:

tmonAState OBJECT-TYPE
SYNTAX DisplayString (SIZE (8))
ACCESS read-only
STATUS mandatory
DESCRIPTION "The current alarm state."
::= {tmonAlarmEntry 4}

The access here is read-only, because the alarm state is set by the alarm input on that alarm point.

Here's an example of an object-type with read-write access:

dpsRTUDateTime OBJECT-TYPE
SYNTAX DisplayString (SIZE (23))
ACCESS read-write
STATUS mandatory
DESCRIPTION "The RTU (Remote Telemetry Unit) system date and time."
::= {dpsRTUIdent 4}

Here the access is read-write, because this is a value that you can set from your SNMP manager. You can retrieve the current settings from the RTU's internal clock through a GetRequest. And if the clock needs to be reset, you can write new data in a SetRequest.