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PRTG Manual: SNMP Custom String Lookup Sensor

The SNMP Custom String Lookup sensor monitors a string that a specific object identifier (OID) returns via the Simple Network Management Protocol (SNMP). It can map the string directly to a sensor status by using a defined lookup file.

Basically, this sensor does a "reverse lookup". You need 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). For more information, see section Example.

For a detailed list and descriptions of the channels that this sensor can show, see section Channel List.

Sensor in Other Languages

Dutch: SNMP Aangepaste Tekst Lookup
French: Recherche chaînes personnalisée (SNMP)
German: SNMP Zeichenfolge mit Lookup
Japanese: SNMP カスタム文字列のルックアップ
Portuguese: Pesquisa da sequência de caracteres (customizado) (SNMP)
Russian: Подстановка пользовательской строки по SNMP
Simplified Chinese: SNMP 自定义字符串查询
Spanish: Búsqueda de cadena (personalizado) (SNMP)

Remarks

Consider the following remarks and requirements for this sensor:

Remark	Description
IPv6	This sensor supports IPv6.
Performance impact	This sensor has a very low performance impact.
Lookups	This sensor uses lookups to determine the status values of one or more channels.
Localhost	It might not work to query data from a probe device via SNMP (querying localhost, 127.0.0.1, or ::1). Add this device with the IP address that it has in your network and create the sensor on this device instead.
Knowledge Base	Knowledge Base: How do I find out which OID I need for an SNMP Custom sensor?

Add Sensor

Setting	Description
Channel Name	Enter a name for the channel in which the sensor shows the results for the OID. Enter a string. You can change this value later in the channel settings of this sensor.

Setting

Description

Channel Name

Enter a name for the channel in which the sensor shows the results for the OID. Enter a string.

You can change this value later in the channel settings of this sensor.

Basic Sensor Settings

The sensor has the following default tags that are automatically predefined in the sensor's settings when you add the sensor:

snmpcustomsensor

For more information about basic sensor settings, see section Sensor Settings.

OID Settings

Setting	Description
OID	Enter the OID of the SNMP object that you want to receive a string from. Most OIDs begin with 1.3.6.1. However, OIDs that start with 1.0, or 1.1, or 1.2 are also allowed. If you want to entirely disable the validation of your entry, add the string norfccheck: to the beginning of the OID, for example, norfccheck:2.0.0.0.1.
Lookup	Select a lookup file that is available in the \lookups\custom subfolder of the PRTG program directory on the probe system. The lookup file must contain all potential strings that the OID can return. You cannot change this value after sensor creation.
If Value Changes	Define what the sensor does when its value changes: Ignore (default): Do nothing. Trigger 'change' notification: Send an internal message that indicates a change. In combination with a change trigger, you can use this to trigger a notification if a change occurs.

Setting

Description

OID

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

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

Lookup

Select a lookup file that is available in the \lookups\custom subfolder of the PRTG program directory on the probe system.

The lookup file must contain all potential strings that the OID can return.

You cannot change this value after sensor creation.

If Value Changes

Define what the sensor does when its value changes:

Ignore (default): Do nothing.
Trigger 'change' notification: Send an internal message that indicates a change.
In combination with a change trigger, you can use this to trigger a notification if a change occurs.

Sensor Display

Setting	Description
Primary Channel	Select a channel from the list to define it as the primary channel. In the device tree, PRTG displays the last value of the primary channel below the sensor's name. The available options depend on what channels are available for this sensor. You can set a different primary channel later by clicking below a channel gauge on the sensor's Overview tab.
Graph Type	Define how this sensor shows different channels: Show channels independently (default): Show a 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 generates a graph that visualizes the different components of your total traffic. You cannot use this option in combination with manual Vertical Axis Scaling (available in the channel settings).
Stack Unit	This setting is only visible if you select Stack channels on top of each other above. Select a unit from the list. PRTG stacks all channels with this unit 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.

Setting

Description

Primary Channel

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

You can set a different primary channel later by clicking below a channel gauge on the sensor's Overview tab.

Graph Type

Define how this sensor shows different channels:

Show channels independently (default): Show a 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 generates a graph that visualizes the different components of your total traffic.
You cannot use this option in combination with manual Vertical Axis Scaling (available in the channel settings).

Stack Unit

This setting is only visible if you select Stack channels on top of each other above.

Select a unit from the list. PRTG stacks all channels with this unit 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 of these settings are inherited from objects that are higher in the hierarchy. We recommend that you change them centrally in the root group settings if necessary. To change a setting for this object only, click under the corresponding setting name to disable the inheritance and to display its options.

For more information, see section Inheritance of Settings.

Example

You must 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 must 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 ("reverse lookup") that is shown, for example, in data graphs. Depending on the integer, the sensor shows the respective status and converts the integer back to the original string to show it as a channel value. If the OID returns a string that the lookup definition does not contain, the sensor shows the 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 the PRTG program directory), and the specified OID returns the string Good. Then the sensor maps the string Good to the integer 0 that is 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 the channel value.

The string match is not case-sensitive.

Use the lookup type SingleInt for this sensor. BitFields and ranges are not supported.

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 that an .oidlib file might contain with your own status definitions. See section Define Lookups for details about this mechanism.

Channel List

Which channels the sensor actually shows might depend on the target device, the available components, and the sensor setup.

Channel	Description
Downtime	In the channel table on the Overview tab, this channel never shows any values. PRTG uses this channel in graphs and reports to show the amount of time in which the sensor was in the Down status.
[Value]	The retrieved string value and its status, as defined in the corresponding lookup file This channel is the primary channel by default.

Channel

Description

Downtime

In the channel table on the Overview tab, this channel never shows any values. PRTG uses this channel in graphs and reports to show the amount of time in which the sensor was in the Down status.

[Value]

The retrieved string value and its status, as defined in the corresponding lookup file

This channel is the primary channel by default.

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