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.
SNMP Custom String Lookup Sensor
For a detailed list and descriptions of the channels that this sensor can show, see section Channel List.
▪Dutch: SNMP Aangepaste Tekst Lookup
▪French: Requête de chaîne 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)
▪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.
▪This sensor supports the IPv6 protocol.
▪This sensor has a very low performance impact.
▪This sensor uses lookups to determine the status values of one or more 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 the channel uses. For details, see section Define Lookups.
▪See section Example for a sample lookup definition for this sensor.
▪See the Knowledge Base: How do I find out which OID I need for an SNMP Custom sensor?
The Add Sensor dialog appears when you manually add a new sensor to a device. It only shows the settings that are required to create the sensor. You can change nearly all settings on the sensor's Settings tab after creation.
OID Settings
Setting |
Description |
|---|---|
Channel Name |
Enter a name for the channel in which the sensor shows the results for the OID. Enter a string.
|
Lookup |
Select a lookup file that is available in the \lookups\custom subfolder of the PRTG program directory on the probe system.
|
Click the Settings tab of a sensor to change its settings.
Basic Sensor Settings
Setting |
Description |
|---|---|
Sensor Name |
Enter a 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 the sensor inherits from its parent device, parent group, and parent probe.
|
Tags |
Enter one or more tags. Confirm each tag with the Spacebar key, a comma, or the Enter key. You can use tags to group objects and use tag-filtered views later on. Tags are not case-sensitive. Tags are automatically inherited.
The sensor has the following default tags that are automatically predefined in the sensor's settings when you add the sensor: ▪snmpcustomsensor |
Priority |
Select a priority for the sensor. This setting determines the position of the sensor in lists. The highest priority is at the top of a list. Choose from the lowest priority ( |
Usually, a sensor connects to the IP Address/DNS Name of the parent device. See the device settings for details. For some sensors, you can explicitly define the monitoring target in the sensor settings.
OID Settings
Setting |
Description |
|---|---|
OID |
Enter the OID of the SNMP object that you want to receive a string from.
|
Lookup |
Shows the lookup file that this sensor uses.
|
If Value Changes |
Define what the sensor does when the sensor value changes: ▪Ignore changes (default): Do nothing. ▪Trigger 'change' notification: Send an internal message indicating that the sensor 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
Setting |
Description |
|---|---|
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 is always displayed below the sensor's name. The available options depend on what channels are available for this sensor.
|
Graph Type |
Define how different channels are shown for this sensor: ▪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. |
Stack Unit |
This setting is only visible if you enable Stack channels on top of each other as Graph Type. Select a unit from the list. All channels with this unit are 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. |
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.
Scanning Interval
For more information, see section Root Group Settings, section Scanning Interval.
Schedules, Dependencies, and Maintenance Window
You cannot interrupt the inheritance for schedules, dependencies, and maintenance windows. The corresponding settings from the parent objects are always active. However, you can define additional schedules, dependencies, and maintenance windows. They are active at the same time as the parent objects' settings.
Schedules, Dependencies, and Maintenance Window
For more information, see section Root Group Settings, section Schedules, Dependencies, and Maintenance Window.
Access Rights
For more information, see section Root Group Settings, section Access Rights.
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.
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
|
KNOWLEDGE BASE
How do I find out which OID I need for an SNMP Custom sensor?
▪https://kb.paessler.com/en/topic/903
What security features does PRTG include?
▪https://kb.paessler.com/en/topic/61108
My SNMP sensors don’t work. What can I do?
▪https://kb.paessler.com/en/topic/46863
PAESSLER TOOLS
MIB Importer
