PRTG Manual: SNMP Custom Table Sensor

The SNMP Custom Table sensor monitors entries from a table that is provided via Simple Network Management Protocol (SNMP). You can create one new sensor per table row. For each sensor, you can define up to ten channels. Each channel shows the value of one defined table column.

  • It can show numerical values in up to 10 channels per table row.

Which channels the sensor actually shows might depend on the monitored device and the sensor setup.

icon-i-roundThe SNMP Library sensor will automatically create SNMP Custom Table sensors when the imported Management Information Base (MIB) file contains tables.

SNMP Custom Table Sensor

SNMP Custom Table Sensor

Click here to enlarge.

Remarks

Add Sensor

The Add Sensor dialog appears when you manually add a new sensor to a device. It only shows the setting fields that are required for creating the sensor. Therefore, you will not see all setting fields in this dialog. You can change (nearly) all settings in the sensor's Settings tab later.

PRTG will create one SNMP Table sensor for each table row that you select in the Add Sensor dialog. The settings you choose will be valid for all sensors that you create when you finish this dialog.

The following settings for this sensor differ in the Add Sensor dialog in comparison to the sensor's settings page.

Snmp Table

Table OID

Enter the OID of the SNMP table you want to monitor. The OID needs to point directly to an object that represents an SNMP table. Once a sensor is created, you cannot change this value. It is shown for reference purposes only. If you need to change this, please add the sensor anew.

icon-i-roundWithout entering an OID, you cannot proceed to the sensor and sensor channel creation.

Basic Sensor Settings

Sensor Name

Enter a meaningful name to identify the sensor. You can use the placeholders [tablename] and [rowidentifier]. They will be replaced with the name of the table and the identifying value of the chosen row respectively. You can choose the column that provides the row identifier in the Identification Column option below.

You can also enter a valid OID that is part of a different SNMP table, for example, [1.3.6.1.2.1.2.2.1.2], to query information that is not contained in the current table. The same index as in the original table will be added to the OID.

Table Specific

Table

Choose the relevant table rows in which you find the data that you want to monitor. You see a list with the names of all items that are available to monitor. Add check marks in front of the respective lines to select the desired items. PRTG creates one sensor for each selection. You can also use the check box in the table head to select and deselect all items.

PRTG shows you the table that the OID you entered before returns. To better find what you want to monitor, especially in large tables, use the search function in the upper right corner.

Identification Column

Define the identification column for the SNMP Table sensor(s) you want to create. The sensor uses this column to uniquely identify each table row. This column should preferably be unique because it will allow the sensor to keep track of changing indexes.

The value of the column that you choose as the identification column will replace the [rowidentifier] in the sensor name. This allows you to distinguish sensors that are created for the same SNMP table.

icon-i-roundOne new sensor is created for each table row you choose.

Sensor Channel #2 – #10

You can create up to 10 different sensor channels for this sensor. You have to define at least one data channel, so you will see all available settings for Sensor Channel #1 without enabling it manually. Additionally you can define Sensor Channel #2 up to Sensor Channel #10. To do so, choose between:

  • Disable: The sensor will not create this channel.
  • Enable: Create an additional channel and define all its characteristics below, its name, column, value type, and unit.

It is not possible to enable or disable sensor channels after the creation of this sensor!

icon-i-roundAll sensor channels that you define while creating an SNMP Table sensor will be the same for all sensors for each table row.

Value Type

Select the expected type of the results in this channel. Choose between:

  • Gauge (unsigned Integer): For integer values, such as 10 or 120.
  • Gauge (signed integer): For integer values, such as -12 or 120.
  • Gauge (float): For float values, such as -5.80 or 8.23.
  • Delta (Counter): For counter values. PRTG will calculate the difference between the last and the current value.

See below for the other channel settings that can be changed also after the sensor has been created.

icon-i-round-redThis sensor monitors numerical values only. Make sure that you do not select columns that return strings because they lead to a Down status. For example, if you monitor an ifTable, we recommend that you do not select an ifDescr column because this will result in an error.

Sensor Settings

On the details page of a sensor, click the Settings tab to change its settings.

icon-i-roundUsually, a sensor connects to the IP Address or DNS Name of the parent device where you created this sensor. See the Device Settings for details. For some sensor types, you can define the monitoring target explicitly in the sensor settings. Please see below for details on available settings.

Basic Sensor Settings

Sensor Name

Enter a meaningful name to identify the sensor. By default, PRTG shows this name in the device tree, as well as in alarms, logs, notifications, reports, maps, libraries, and tickets.

Parent Tags

Shows Tags that this sensor inherits from its parent device, group, and probe. This setting is shown for your information only and cannot be changed here.

Tags

Enter one or more Tags, separated by spaces or commas. You can use tags to group sensors and use tag–filtered views later on. Tags are not case sensitive. We recommend that you use the default value.

You can add additional tags to the sensor if you like. Other tags are automatically inherited from objects further up in the device tree. These are visible above as Parent Tags.

Priority

Select a priority for the sensor. This setting determines where the sensor is placed in sensor lists. Top priority is at the top of a list. Choose from one star (low priority) to five stars (top priority).

Snmp Table

Table OID

Shows the OID of the SNMP table that this sensor monitors. Once a sensor is created, you cannot change this value. It is shown for reference purposes only. If you need to change this, please add the sensor anew.

Table Specific

Identifier

This is the value of the column that you selected as the Identification Column during the sensor creation. It is also displayed in the sensor name to distinguish it from other sensors you created for the same table with other table rows. You can change the identifier if you want to.

Identification Column

Shows the table column that you chose as the identification column. Once a sensor is created, you cannot change this value. It is shown for reference purposes only. If you need to change this, please add the sensor anew.

Sensor Channel #x Name

Enter a name for the channel in which the sensor shows the desired result. Please enter a string.

Sensor Channel #x Column

Select the table column that together with the table row points to the value that you want to monitor in this channel. You can choose between the available columns of the table that you monitor.

Sensor Channel #x Value Type

Shows the value type of the data that this sensor receives in this channel. Once a sensor is created, you cannot change this value. It is shown for reference purposes only. If you need to change this, please add the sensor anew.

Sensor Channel #x Unit

Define the unit of the data that this sensor receives in this channel. Choose between:

  • BytesBandwidth
  • BytesMemory
  • BytesDisk
  • Temperature
  • Percent
  • TimeResponse
  • TimeSeconds
  • TimeHours
  • Count
  • CPU
  • BytesFile
  • SpeedDisk
  • SpeedNet
  • Custom
  • Value Lookup

icon-book-arrowsFor more information about the available units, see the PRTG Application Programming Interface (API) Definition for custom sensors.

icon-i-round-redTo use lookups with this channel, choose the unit Value Lookup and select your lookup file below. Do not use the unit Custom for using lookups with this sensor and do not use the channel settings to define a lookup file!

Sensor Channel #x Custom Unit

This setting is only visible if you select the Custom unit option above. Define a unit for the channel value. Please enter a string.

Sensor Channel #x Value Lookup

This setting is only visible if you select the Value Lookup option above. Select a lookup file that you want to use with this channel.

Sensor Channel #x+1

Shows if you enabled or disabled a channel. Once a sensor is created, you cannot change this value. It is shown for reference purposes only. If you need to change this, please add the sensor anew.

Sensor Display

Primary Channel

Select a channel from the list to define it as the primary channel. In the device tree, the last value of the primary channel will always be displayed below the sensor's name. The available options depend on what channels are available for this sensor.

icon-i-roundYou can set another primary channel later by clicking the pin symbol of a channel in the sensor's Overview tab.

Graph Type

Define how different channels will be shown for this sensor.

  • Show channels independently (default): Show an own graph for each channel.
  • Stack channels on top of each other: Stack channels on top of each other to create a multi-channel graph. This will generate an easy-to-read graph that visualizes the different components of your total traffic.
    icon-i-roundThis option cannot be used in combination with manual Vertical Axis Scaling (available in the Sensor Channels Settings settings).

Stack Unit

This setting is only available if stacked graphs are selected above. Choose a unit from the list. All channels with this unit will be stacked on top of each other. By default, you cannot exclude single channels from stacking if they use the selected unit. However, there is an advanced procedure to do so.

Inherited Settings

By default, all following settings are inherited from objects higher in the hierarchy and should be changed there, if necessary. Often, best practice is to change them centrally in the Root group's settings, see section Inheritance of Settings for more information. To change a setting only for this object, disable inheritance by clicking the button next to inherit from under the corresponding setting name. You will then see the options described below.

Scanning Interval

Click inherited_settings_button to disrupt the inheritance. See section Inheritance of Settings for more information.

Scanning Interval

Select a scanning interval (seconds, minutes, or hours) from the list. The scanning interval determines the time the sensor waits between two scans. You can change the available intervals in the system administration on PRTG on premises installations.

If a Sensor Query Fails

Define the number of scanning intervals that a sensor has time reach and check a device again in case a sensor query fails. The sensor can try to re-reach and check a device several times, depending on the option you select here, before it will be set to a Down status. This helps you avoid false alarms if the monitored device has only temporary issues. For previous scanning intervals with failed requests, the sensor will show a Warning status. Choose between:

  • Set sensor to "down" immediately: The sensor will show an error immediately after the first failed request.
  • Set sensor to "warning" for 1 interval, then set to "down" (recommended): After the first failed request, the sensor will show a yellow warning status. If the following request also fails, the sensor will show an error.
  • Set sensor to "warning" for 2 intervals, then set to "down": Show an error status only after three continuously failed requests.
  • Set sensor to "warning" for 3 intervals, then set to "down": Show an error status only after four continuously failed requests.
  • Set sensor to "warning" for 4 intervals, then set to "down": Show an error status only after five continuously failed requests.
  • Set sensor to "warning" for 5 intervals, then set to "down": Show an error status only after six continuously failed requests.

icon-i-roundSensors that monitor via Windows Management Instrumentation (WMI) always wait at least one scanning interval until they show an error. It is not possible to set a WMI sensor to "down" immediately, so the first option will not apply to these sensor types. All other options can apply.

icon-i-roundIf a sensor has defined error limits for channels, it will always show a Down status immediately, so no "wait" option will apply.
 

icon-i-roundIf a channel uses lookup values, it will always show a Down status immediately, so no "wait" options will apply.

Schedules, Dependencies, and Maintenance Window

icon-i-roundInheritance for schedules, dependencies, and maintenance windows cannot be interrupted. The corresponding settings from the parent objects will always be active. However, you can define additional settings here. They will be active at the same time as the parent objects' settings.

Schedule

Select a schedule from the list. Schedules can be used to monitor for a certain time span (days, hours) every week. With the period list option it is also possible to pause monitoring for a specific time span. You can create new schedules and edit existing ones in the account settings.

icon-i-roundSchedules are generally inherited. New schedules will be added to existing ones, so all schedules are active at the same time.

Maintenance Window

Specify if you want to set up a one-time maintenance window. During a "maintenance window" period, this object and all child objects will not be monitored. They will be in a paused state instead. Choose between:

  • Not set (monitor continuously): No maintenance window will be set and monitoring will always be active.
  • Set up a one-time maintenance window: Pause monitoring within a maintenance window. You can define a time span for a monitoring pause below and change it even for a currently running maintenance window.

icon-i-roundTo terminate a current maintenance window before the defined end date, change the time entry in Maintenance Ends field to a date in the past.

Maintenance Begins

This field is only visible if you enabled the maintenance window above. Use the date time picker to enter the start date and time of the maintenance window.

Maintenance Ends

This field is only visible if you enabled the maintenance window above. Use the date time picker to enter the end date and time of the maintenance window.

Dependency Type

Define a dependency type. Dependencies can be used to pause monitoring for an object depending on the status of another. You can choose between:

  • Use parent: Pause the current sensor if the device, where it is created on, is in Down status, or is paused by another dependency.
  • Select object: Pause the current sensor if the device, where it is created on, is in Down status, or is paused by another dependency. Additionally, pause the current sensor if a specific other object in the device tree is in Down status, or is paused by another dependency. Select below.
  • Master object for parent: Make this sensor the master object for its parent device. The sensor will influence the behavior of the device, where it is created on: If the sensor is in Down status, the device will be paused. For example, it is a good idea to make a Ping sensor the master object for its parent device to pause monitoring for all other sensors on the device in case the device cannot even be pinged. Additionally, the sensor will be paused if the parent group of its parent device is in Down status, or if it is paused by another dependency.

icon-i-roundTesting your dependencies is easy! Simply choose Simulate Error Status from the context menu of an object that other objects depend on. A few seconds later all dependent objects should be paused. You can check all dependencies in your PRTG installation by selecting Devices | Dependencies from the main menu bar.

Dependency

This field is only visible if the Select object option is enabled above. Click on the reading-glasses and use the object selector to choose an object on which the current sensor will depend.

Dependency Delay (Sec.)

Define a time span in seconds for a dependency delay. After the master object for this dependency goes back to Up status, PRTG will start monitoring the depending objects after this extra delayed. This can help to avoid false alarms, for example, after a server restart, by giving systems more time for all services to start up. Please enter an integer value.

icon-i-round-redThis setting is not available if you choose this sensor to Use parent or to be the Master object for parent. In this case, please define delays in the parent Device Settings or in the superior Group Settings.

Access Rights

Click inherited_settings_button to disrupt the inheritance. See section Inheritance of Settings for more information.

User Group Access

Define which user group(s) will have access to the object you're editing. A table with user groups and types of access rights is shown: It contains all user groups from your setup. For each user group you can choose from the following access rights:

  • Inherited: Use the access rights settings of the parent object.
  • None: Users in this group cannot see or edit the object. The object neither shows up in lists nor in the device tree. Exception: If a child object is visible to the user, the object is visible in the device tree, though not accessible.
  • Read: Users in this group can see the object and review its monitoring results.
  • Write: Users in this group can see the object, review its monitoring results, and edit the object's settings. They cannot edit access rights settings.
  • Full: Users in this group can see the object, review its monitoring results, edit the object's settings, and edit access rights settings.

You can create new user groups in the System Administration—User Groups settings. To automatically set all objects further down in the hierarchy to inherit this object's access rights, set a check mark for the Revert children's access rights to inherited option.

icon-book-arrowsFor more details on access rights, see the section User Access Rights.

More

Knowledge Base: What can I monitor with the SNMP Custom Table Sensor?

Knowledge Base: How to monitor a no-break (UPS) device complying to the UPS-MIB (RFC 1628)

Knowledge Base: How do I find out what OID I need to use for a custom sensor?

Knowledge Base: My SNMP sensors don't work. What can I do?

Edit Sensor Channels

To change display settings, spike filter, and limits, switch to the sensor's Overview tab and click the gear icon of a specific channel. For detailed information, see the Sensor Channels Settings section.

Notifications

Click the Notifications tab to change notification triggers. For detailed information, see the Sensor Notifications Settings section.

Others

For more general information about settings, see the Object Settings section.

Sensor Settings Overview

For information about sensor settings, see the following sections: