SNMP Polling

SNMP polling refers to synchronous process of sampling the status of an external device using SNMP get operations.

SNMP polling is implemented by Iotellect as Device synchronization procedure.

The synchronization procedure uses parameters specified in SNMP Settings to perform SNMP operations. There are two types of synchronization that can be applied to monitored devices.

Full SNMP synchronization includes the following steps:

• Checking SNMP communication with the monitored device. This is performed by connecting to the device and sampling one SNMP variable.
• Reading device metadata and variable values by performing SNMP Walk.

SNMP walk is an operation that uses SNMP GETNEXT requests to query all the variable available at the monitored device and their values.

• Correlating obtained metadata with MIB Files Directory entries to get more information about each setting (its type, description etc.).
• Converting SNMP device settings into Iotellect Server Context Variables and creating the Settings Cache.
• Storing obtained data in settings cache. Refer to SNMP Polling Results section for detailed description of how SNMP monitoring results are presented by device driver.

The SNMP monitoring service is considered Online if all operations are successfully performed. Any error encountered during synchronization is saved in monitoring results and renders the service Offline.

Notice that SNMP walk operation provides a list SNMP variables along with their values. Thus no additional steps are required to synchronize particular variables. On the other hand, SNMP walk is a long operation. Therefore it is not performed during the very first device synchronization. Thus, service just checks that SNMP communications is supported by the managed device and quickly reports the result as service status. Full synchronization is issued right after the first synchronization completes. This method eliminates long synchronization delays for newly added devices.

If there is no need to re-read all the device metadata and merely several known variables should be refreshed full synchronization is not performed. Instead, only these variables are polled using SNMP get operations and device cache is updated accordingly.

For monitored devices which return data tables in polling response, setting the SNMP table filter allows both rows and columns to be omitted either explicitly or dynamically via expression. Global default table filters can be specified for new device instances, as well as specifying filters per device.

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