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Aurelio, System Admin at Paessler AG

The SNMP Custom String Lookup sensor monitors a string that a specific Object Identifier (OID) returns via Simple Network Management Protocol (SNMP). It can map the string directly to a sensor status by using a defined lookup file. Basically, this sensor type does a "reverse lookup". You have to define all potential return strings in the lookup file as text values, each in one lookup entry. Graphs and data tables show the value to which the string is mapped, usually an integer (lookup type SingleInt). See section Example below.

  • This sensor shows a retrieved string value and its status, as defined in the corresponding lookup file.
     
SNMP Custom Lookup SensorSNMP Custom Lookup Sensor

Click here to enlarge: http://media.paessler.com/prtg-screenshots/snmp_custom_lookup.png

Remarks

  • See manual section SNMP Custom String Lookup Sensor—Example for a sample lookup definition for this sensor type.
  • Note: It might not work to query data from a probe device via SNMP (querying localhost , 127.0.0.1 , or ::1 ). Add this device to PRTG with the IP address that it has in your network and create the SNMP sensor on this device instead.
  • Knowledge Base: How do I find out what OID I need to use for a custom sensor?
  • This sensor type uses lookups to determine the status values of one or more sensor channels. This means that possible states are defined in a lookup file. You can change the behavior of a channel by editing the lookup file that this channel uses. For details, please see the manual section Define Lookups.
  • For a general introduction to the technology behind SNMP, please see the manual section Monitoring via SNMP.
  • Important notice: Currently, this sensor type is in beta status. The methods of operating can change at any time, as well as the available settings. Do not expect that all functions will work properly, or that this sensor works as expected at all. Be aware that this type of sensor can be removed again from PRTG at any time.

Add Sensor

The Add Sensor dialog appears when adding a new sensor to a device manually. 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.

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

OID Values

Channel Name

Enter a name for the channel in which the sensor shows the results at the given OID. Please enter a string. You can change this value later in the respective channel settings of this sensor.

Lookup

Select a lookup file that you stored in the \lookups\custom subfolder of your PRTG installation. This lookup file must contain all potential strings that the monitored OID can return.

Sensor Settings

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

Note: Usually, a sensor connects to the IP Address or DNS Name of the parent device on which 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 space or comma. 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 it, 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).

OID Values

OID Value

Enter the OID of the SNMP object you want to receive a string from.

Note: Most OIDs begin with 1.3.6.1 . However, entering OIDs starting with 1.0 , or 1.1 , or 1.2 is also allowed. If you want to disable the validation of your entry entirely, add the string norfccheck: at the beginning of your OID, for example, norfccheck:2.0.0.0.1 .

Lookup

Shows the lookup file that this sensor uses. 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.

If Value Changes

Define what this sensor will do when the sensor value changes. You can choose between:

  • Ignore changes (default) : The sensor takes no action on change.
  • Trigger 'change' notification : The sensor sends an internal message indicating that its value has changed. In combination with a Change Trigger , you can use this mechanism to trigger a notification whenever the sensor value changes.

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. Note: You can set another primary channel later by clicking on 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 which visualizes the different components of your total traffic. Note: This 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. To change a setting only for this object, disable inheritance by clicking on the check mark before the corresponding setting name. You will then see the options described below.

Scanning Interval

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.

When a Sensor Reports an Error

Define the number of scanning intervals that a sensor has time to report an error before the sensor will be set to a Down status. The sensor can try to reach a device several times, depending on the setup you can specify here, to help 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.

Note: Sensors 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 "down" immediately, so the first option will not apply to these sensor types (all other options can apply).

Note: If a sensor has defined error limits for channels, this sensor will always be set to a Down status immediately, so no "wait" option will apply.

Note: If a channel uses lookup values, the sensor will always be set to a Down status immediately, so no "wait" options will apply.

Schedules, Dependencies, and Maintenance Window

Note: Inheritance 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.

Note: Schedules 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.

Note: To 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.

Note: Testing 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.

Note: This 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

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.

For more details on access rights, please see the section User Access Rights .

Example

You have to provide all possible return strings for this sensor in one lookup file. For example, consider an OID that can return one of the three strings Good , Deficient , or Bad . Then you have to define a lookup file for this sensor that contains all these possible string values as text, each text value in one lookup entry:
 

<?xml version="1.0" encoding="UTF-8"?>
<ValueLookup id="mylookupfile" desiredValue="0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="PaeValueLookup.xsd">
 <Lookups>
                      <SingleInt state="Ok" value="0">
                Good
                      </SingleInt>
                      <SingleInt state="Warning" value="1">
                Deficient
                      </SingleInt>
           <SingleInt state="Error" value="2">
                Bad
                      </SingleInt>
    </Lookups>
</ValueLookup>

 
If a retrieved string matches one of the text values, the sensor maps it into the defined integer value ("reverse lookup") that is shown, for example, in data graphs. Depending on the integer, the sensor shows the according status and converts the integer back to the original string to show it as channel value. If the OID returns a string that the lookup definition does not contain, the sensor shows a Down status with a corresponding error message.

For example, you create an SNMP Custom String Lookup sensor, apply the example lookup definition from above (store it into the \lookups\custom subfolder of your PRTG installation), and the given OID returns the string Good . Then the sensor maps Good into the integer value 0 , shown in the live graph of the sensor, for example. According to the status definition state="Ok" , the sensor status is Up in this case. The integer 0 is converted back to the string Good which is shown as channel value.

Note: The string match is not case sensitive.

Note: Please use the lookup type SingleInt for this sensor. BitFields and ranges are not supported!

Note: If you imported an SNMP library (this is an oidlib file) that contains lookups (you can see this in section Lookup in the MIB Importer), you can define your own sensor states for returning values. Use the lookupname of the imported SNMP library as id parameter in a custom lookup definition. This overrides the lookups which an oidlib might contain with your own status definitions. See section Define Lookups—Customizing Lookups for details about this mechanism.

More

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, please see the Sensor Channels Settings section.

Notifications

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

Others

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

Sensor Settings Overview

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