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 many parameters can be monitored with it. PRTG provides you with around 70 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 device that you want to monitor 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.

icon-i-roundIf you are uncertain whether SNMP is enabled on the target device and works, we recommend that you try our SNMP Tester, designed for just this purpose. You can scan for uptime to perform a basic check for SNMP availability of the target device.

Setup Checklist

  1. Enable SNMP on the device.
  2. Allow access to SNMP for the machine running PRTG Network Monitor in the security settings of the device.
  3. Allow User Datagram Protocol (UDP) packages to be sent bidirectional from the PRTG core server to the device you want to monitor.
  4. SNMP requires the use of UDP ports >1023 to the PRTG client side. This is important for your firewall settings.
  5. Ensure that the firmware of the monitored device is up to date.
  6. Select the appropriate SNMP protocol.

icon-i-roundIt is important to know which SNMP version you have to select, because if it is not supported by the server or device you want to monitor, you receive an error message.

icon-book-bulbFor more information, see this Knowledge Base article: General Introduction to SNMP and PRTG

SNMP Monitoring Overview

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
  • Poseidon
  • QNAP
  • SonicWall
  • Synology

icon-book-bulbFor more information, see this article in our 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

The SNMP CPU Load sensor monitors the system load using the Simple Network Management Protocol (SNMP).

The sensor can show the following:

  • Load of several CPUs in percent

SNMP Disk Free sensor

The SNMP Disk Free sensor monitors the free disk space on a logical disk via the Simple Network Management Protocol (SNMP).

The sensor can show the following:

  • Free disk space in percent
  • Free disk space in bytes
  • Total disk space

SNMP Hardware Status sensor

The SNMP Hardware Status sensor monitors the status of a server's hardware component via the Simple Network Management Protocol (SNMP).

The sensor can show the following:

  • Current status of the monitored hardware component
  • Number of errors per time period

SNMP Memory sensor

The SNMP Memory sensor monitors the memory usage of a system via the Simple Network Management Protocol (SNMP).

The sensor can show the following:

  • Available memory in bytes
  • Available memory in percent
  • Total memory

SNMP Printer sensor

The SNMP Printer sensor is a generic sensor that monitors various types of printers via the Simple Network Management Protocol (SNMP).

The sensor can show the following:

  • Total number of printed pages
  • Fill level of cartridges and toners
  • Status of the printer cover

Additionally, the sensor shows the printer status as sensor message.

SNMP RMON sensor

The SNMP RMON sensor monitors traffic on a device using the Remote Monitoring (RMON) standard via the Simple Network Management Protocol (SNMP). You can create it on an SNMP-compatible device that provides traffic data via RMON. Depending on the data that your device returns, PRTG displays traffic data for each port in different channels, which allows a detailed analysis. If available, the sensor queries 64-bit counters.

The sensor can show the following for each port:

  • Transmitted kbit/s
  • Packets (#/s)
  • Broadcast Packets (#/s)
  • Multicast Packets (#/s)
  • Cyclic redundancy check (CRC) Errors (#/s)
  • Undersize Packets (#/s)
  • Oversize Packets (#/s)
  • Fragments (#/s)
  • Jabbers (#/s)
  • Collisions (#/s)
  • Packets <= 64 Byte (#/s)
  • Packets 65 - 127 Bytes (#/s)
  • Packets 128 - 255 Bytes (#/s)
  • Packets 256 - 511 Bytes (#/s)
  • Packets 512 - 1023 Bytes (#/s)
  • Packets 1024 - 1518 Bytes (#/s)
  • Drop Events (#/s)

SNMP System Uptime sensor

The SNMP System Uptime sensor monitors the time that a device runs via the Simple Network Management Protocol (SNMP).

The sensor can show the following:

  • System uptime of the monitored device

SNMP Traffic sensor

The SNMP Traffic sensor monitors traffic on a device using the Simple Network Management Protocol (SNMP). You can create it on a device that provides traffic data. PRTG creates one traffic sensor for each individual port.

The sensor can show the following:

  • Traffic in
  • Traffic out
  • Traffic total

You can also add additional channels:

  • Errors in and out
  • Discards in and out
  • Unicast packets in and out
  • Non-unicast packets in and out
  • Multicast packets in and out
  • Broadcast packets in and out
  • Unknown protocols

SNMP Trap Receiver sensor

The SNMP Trap Receiver sensor receives and analyzes Simple Network Management Protocol (SNMP) traps.

The sensor can show the following:

  • Overall number of received traps per second
  • Trap messages categorized as "warning" per second
  • Trap messages categorized as "error" per second
  • Number of dropped trap packets per second on the SNMP trap collector port
  • The actual trap messages

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

What it monitors

SNMP Linux Disk Free sensor

The SNMP Linux Disk Free sensor monitors free space on disks of a Linux/Unix system using the Simple Network Management Protocol (SNMP).

The sensor can show the following:

  • Free total disk space in bytes
  • Free space in bytes for every mounted partition
  • Free space in percent for every mounted partition
  • Free inodes in percent for every mounted partition

SNMP Linux Load Average sensor

The SNMP Linux Load Average sensor monitors the system load average of a Linux/Unix system using the Simple Network Management Protocol (SNMP).

The sensor can show the following:

  • Average system load within a 1-minute scanning interval
  • Average system load within a 5-minute scanning interval
  • Average system load within a 15-minute scanning interval

SNMP Linux Meminfo sensor

The SNMP Linux Meminfo sensor monitors the memory usage of a Linux/Unix system using the Simple Network Management Protocol (SNMP).

The sensor can show the following:

  • Available memory in absolute and percentage values
  • Used physical memory (free memory plus buffer plus cache) in percent
  • Free physical memory (free memory plus buffer plus cache) in bytes
  • Used swap memory in percent
  • Free swap memory in bytes
  • Used memory on the whole system (physical memory plus swap) in percent
  • Free memory on the whole system (physical memory plus swap) in bytes

SNMP Linux Physical Disk sensor

The SNMP Linux Physical Disk sensor monitors the input/output (I/O) on disks of a Linux/Unix system using the Simple Network Management Protocol (SNMP).

The sensor can show the following:

  • Read bytes per second
  • Written bytes per second
  • Number of read accesses per second
  • Number of write accesses per second

SNMP Windows Service sensor

The SNMP Windows Service sensor monitors a Windows service via the Simple Network Management Protocol (SNMP).

The sensor can show the following:

  • Operating status of the monitored service

Custom SNMP Sensors

PRTG also offers custom SNMP sensors. The monitoring capabilities of these sensors extend the scope of the generic sensors. With the 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 just need to find out the required OIDs for your desired device readings, for example, in the vendor’s documentation of your hardware device.

icon-book-bulbFor more details, see the Knowledge Base: How do I find out which OID I need for an SNMP Custom sensor?

Sensor

What it monitors

SNMP Custom sensor

The SNMP Custom sensor monitors a single parameter that is returned by a specific object identifier (OID) using the Simple Network Management Protocol (SNMP).

The sensor can show the following:

  • A single numerical value (int64) for a specified OID

Value types include the expected numeric type of the results at the specified OID: You can choose from

  • Absolute (unsigned integer): for integer values such as 10 or 120
  • Absolute (signed integer): for integer values 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.

icon-cameraFor more information, see this video tutorial SNMP Custom Sensor and Custom Library Sensor on our website.

SNMP Custom Advanced sensor

The SNMP Custom Advanced sensor monitors numerical values returned for object identifiers (OID) using the Simple Network Management Protocol (SNMP).

The sensor can show the following:

  • Numerical values for specified OIDs (up to 10 OIDs are possible) that refer to a specific SNMP device

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) using the Simple Network Management Protocol (SNMP). It can check for keywords. If you want to set limits to the sensor channel value, you can also extract a numeric value contained in the string.

The sensor can show the following:

  • Response time of the monitored device
  • A value extracted from the string (optionally)

In the sensor message, the sensor shows the string you search for and the reason for a current Warning or Down status.

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 numerical value from the string that can be evaluated later for additional alerts.

icon-book-arrowsSee 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 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). For more information, see section SNMP Custom String Lookup Sensor—Example.

The sensor can show the following:

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

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.

The sensor can show the following:

  • Numerical values in up to 10 channels per table row

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.

icon-book-bulbFor 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 compiled Management Information Base (MIB) file to create sensors that monitor a device via the Simple Network Management Protocol (SNMP). This approach provides custom monitoring beyond the standard SNMP sensors of PRTG.

The content of the MIB file determines which data types are available for monitoring. When you create the sensor, it provides a list of counters that came back from the target device based on checking every object identifier (OID) in the MIB file. From this list, you can select what you want to monitor.

The SNMP Library sensor automatically creates the following custom SNMP sensors based on the data types available in the MIB file:

icon-i-roundThe SNMP Library sensor is not actually a sensor and does not appear as a running sensor. It is a sensor that uses the meta-scan facility of the PRTG probe to find or match OIDs from the compiled MIB file and makes the creation of custom sensors easier because you do not have to manually enter the OIDs.

To monitor SNMP-capable devices and add sensors using the SNMP Library sensor, download the manufacturer's MIB files for the target device, convert the MIB files to the OID library format, and import them into PRTG. PRTG also provides precompiled .oidlib files that already contain the OIDs of SNMP counters for the most common devices in a network.

icon-book-bulbFor more information, see the Knowledge Base: How do SNMP, MIBs and OIDs work?

Default .oidlib Files Overview

PRTG includes the following files that you can use with the SNMP Library sensor. These files allow extending your SNMP monitoring to many devices. Note that not all devices and/or parameters may be supported by the libraries.

.OIDLIB FILE

DESCRIPTION

APC UPS.oidlib

Can be used to monitor uninterruptible power supplies (UPS) from APC American Power Conversion Corp.

APCSensorstationlib.oidlib

Can be used to monitor alarm status, communication status, humidity, and temperature as shown by an APC sensor station.

Basic Linux Library (UCD-SNMP-MIB).oidlib

Can be used to monitor basic system parameters on Linux systems, such as memory, disk and swap, CPU, and more.

cisco-interfaces.oidlib

Can be used to monitor Cisco-specific parameters, for example, the number of present network interfaces on a system, several states of an interface (admin, oper, speed, type, errors, discards, etc.), and more.

cisco-queue.oidlib

Can be used to monitor queues on a Cisco interface, for example, queue depth and its maximum, discarded messages from the queue, the number of the queue within the queue set, and more.

Dell Storage Management.oidlib

Can be used to monitor Dell storage devices. Possible parameters include disk arrays, battery and power supply, fan and temperature, virtual disk, and more.

Dell Systems Management Instrumentation.oidlib

Can be used to monitor the hardware of Dell systems. Possible parameters include ACPower and battery, alerts, base board, BIOS, Baseboard Management Controller (BMC), chassis, COO, cooling, event log, firmware, integrated development environment (IDE), keyboard, memory, port, network, processor, Small Computer System Interface (SCSI), system, temperature, USB, universally unique identifier (UUID), and more.

HP LaserJet Status.oidlib

Can be used to monitor toner, paper, and jam status of an HP LaserJet printer.

Linux SNMP (AX BGP DisMan EtherLike Host).oidlib

Can be used to monitor different aspects of Linux systems.

icon-i-roundThis file may detect a very large number of interfaces. It may take a few seconds until the selection table is shown.

Linux SNMP (Framework Proxy Noti v2).oidlib

Can be used to monitor different aspects of Linux systems.

icon-i-roundThis file may detect a very large number of interfaces. It may take a few seconds until the selection table is shown.

Linux SNMP (IP Net SNMP Noti OSPF RMON SMUX).oidlib

Can be used to monitor different aspects of Linux systems.

icon-i-roundThis file may detect a very large number of interfaces. It may take a few seconds until the selection table is shown.

Linux SNMP (Source TCP UCD UDP).oidlib

Can be used to monitor different aspects of Linux systems.

icon-i-roundThis file may detect a very large number of interfaces. It may take a few seconds until the selection table is shown

Paessler Common OID Library.oidlib

Can be used to monitor many common hardware devices. It is used for several sensors and is encrypted.

SNMP Informant std.oidlib

Can be used to monitor logical disks, processor, memory, and network interface on Windows systems.

More

Knowledge Base: How do SNMP, MIBs and OIDs work?

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

Knowledge Base: How can I import my MIB files into PRTG?

Knowledge Base: Can't find a sensor for my device in PRTG but I believe it supports SNMP. How to proceed?