PRTG Manual: Choosing the Right SNMP Sensor

The Simple Network Management Protocol (SNMP) generally requires little configuration once it is set up. Many network devices support it and you can monitor many parameters with it. PRTG provides you with various SNMP sensors. These sensors range from monitoring general parameters to very specific parameters. Choosing the right sensor for SNMP monitoring that gives you the desired hardware parameters is a decision that depends on several factors: the type of hardware you have, what values you want to monitor, and a few others.

Check SNMP Capability

Make sure that each target device supports SNMP, and that SNMP is enabled. You can find out whether a device supports SNMP by either going to the vendor’s website or checking that it is enabled in the configuration of the device.

If you are uncertain whether SNMP is enabled on the target device and works, we recommend that you try SNMP Tester. You can scan for uptime to perform a basic check for SNMP availability of the target device.

Setup Checklist

Enable SNMP on the device.
In the security settings of the device, allow SNMP access for the PRTG core server system.
Allow User Datagram Protocol (UDP) packages to be sent bidirectionally from the PRTG core server to the device.
SNMP requires the use of UDP ports >1023 to the PRTG client side. This is important for your firewall settings.
Ensure that the firmware of the device is up to date.
Select the appropriate SNMP protocol.

It is important to know which SNMP version you need to select, because if it is not supported by the server or device you want to monitor, you receive an error message.

For more information, see the Knowledge Base: My SNMP sensors don’t work. What can I do?

SNMP Monitoring Overview

Vendor-specific SNMP Sensors

PRTG offers many vendor-specific SNMP sensors for some common vendors. These sensors are programmed to match the respective end devices. There are also workarounds for known vendor implementation issues, for example, if SNMP has not been fully implemented on an end device according to the RFCs. Here, our vendor-specific sensors still automatically receive the most important values.

Supported Vendors

APC
Buffalo
Cisco
Dell
Fujitsu
HP
HPE
IBM
Jacarta
Juniper
LenovoEMC
NetApp
Nutanix
Poseidon
QNAP
Rittal
SonicWall
Synology

For more information, see the Knowledge Base: What SNMP sensors does PRTG offer?

Generic SNMP Sensors

PRTG offers several generic sensors that work with almost every device that supports SNMP, the corresponding Management Information Base (MIB) file and OIDs, and it correctly implements the respective RFCs. The standard SNMP libraries of PRTG include predefined, common values for the generic SNMP sensors. You can monitor the following parameters with the generic sensors.

Sensor	What It Monitors
SNMP CPU Load sensor	System load via SNMP
SNMP Disk Free sensor	Free disk space on a logical disk via SNMP
SNMP Hardware Status sensor	Status of a hardware component of a server via SNMP
SNMP Memory sensor	Memory usage of a system via SNMP
SNMP Printer sensor	Various types of printers via SNMP
SNMP RMON sensor	Traffic on a device using RMON via SNMP
SNMP System Uptime sensor	Uptime of a device via SNMP
SNMP Traffic sensor	Traffic on a device via SNMP
SNMP Trap Receiver sensor	SNMP traps

Operating System-based SNMP Sensors

PRTG also offers several operating system-based SNMP sensors that extend your SNMP monitoring. You can monitor the following parameters with these sensors.

Sensor	Description
SNMP Linux Disk Free sensor	Free space on disks of a Linux/Unix system via SNMP
SNMP Linux Load Average sensor	System load average of a Linux/Unix system via SNMP
SNMP Linux Meminfo sensor	Memory usage of a Linux/Unix system via SNMP
SNMP Linux Physical Disk sensor	I/O on disks of a Linux/Unix system via SNMP
SNMP Windows Service sensor	Windows service via SNMP

Custom SNMP Sensors

PRTG also offers custom SNMP sensors. The monitoring capabilities of these sensors extend the scope of the generic sensors. With custom sensors, you can show certain values that are not included in the standard libraries of PRTG. With these sensors, you can monitor most devices that support SNMP and for which PRTG does not have native sensors. Basically, you only need to find out the required OIDs for the desired device readings, for example, in the vendor’s documentation for your hardware device.

For more information, see the Knowledge Base: How do I find out which OID I need for an SNMP Custom sensor?

Sensor	Description
SNMP Custom sensor	The SNMP Custom sensor monitors a single parameter that is returned by a specific object identifier (OID) via the Simple Network Management Protocol (SNMP). Value types include the expected numeric type of the results at the specified OID: You can choose from Absolute (unsigned integer): for integers such as 10 or 120 Absolute (signed integer): for integers such as -12 or 120 (negative values supported) Absolute (float): for float values such as -5.80 or 8.23 (with decimal places) Delta (counter): PRTG calculates the difference between the previous and the current value. For more information, see this video tutorial SNMP Custom sensor and SNMP Custom Library sensor on our website.
SNMP Custom Advanced sensor	The SNMP Custom Advanced sensor monitors numeric values returned for object identifiers (OID) via the Simple Network Management Protocol (SNMP). This sensor monitors very similarly to the regular SNMP Custom sensor, with the advantage of being able to poll up to 10 specific OIDs with a single sensor. For each OID, you can define a name, OID, expected type, and the unit to be displayed. The possible value types are the same as with the SNMP Custom sensor.
SNMP Custom String sensor	The SNMP Custom String sensor monitors a string returned by a specific object identifier (OID) via the Simple Network Management Protocol (SNMP). It can check for keywords. If you want to set limits to the channel value, you can also extract a numeric value contained in the string. Hexadecimal-encoded strings can also be decoded as MAC addresses or IP addresses. The sensor can check for keywords via plain text or regular expression (regex) or you can use a regex to extract a numeric value from the string that can be evaluated later for additional alerts. See section Number Extraction with Regular Expression for an example.
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 Table sensor	The SNMP Custom Table sensor monitors entries from a table that is provided via the 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. Vendors use tables when there are multiple instances of the same object (for example, memory, disks). The sensor recognizes a table via a meta-scan and lets you configure the indexes (interfaces) that you want to monitor. For more details, see the Knowledge Base: What can I monitor with the SNMP Custom Table sensor?
SNMP Library sensor	The SNMP Library sensor uses a Management Information Base (MIB) file to create sensors that monitor a device via the Simple Network Management Protocol (SNMP).