PRTG Manual: Choosing the Right SNMP Sensor

The Simple Network Management Protocol (SNMP) is easy to use and generally requires little configuration once it is set up. Many network devices support it and many parameters can be monitored with it. So to help cover all of your monitoring needs, 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 you want to monitor supports SNMP, and that it is enabled. You can find out whether SNMP is supported by a device by either going to the vendor’s website or check 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 device's security settings.
  3. Allow User Datagram Protocol (UDP) packages to travel from the machine running PRTG to the device you want to monitor and back.
  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 will receive an error message.

icon-book-bulbSee this article in our Knowledge Base for more information: 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 have been tailored to fit the end devices perfectly. Many years of experience allow us to work around familiar vendor implementation errors, for example if SNMP has not been fully implemented on an end device according to the RFCs. In this case, our vendor specific sensors still automatically receive the most important values with little to no effort on your part (looking for Object Identifiers (OIDs), for example). These sensors take care of everything for you.

Supported Vendors

  • APC
  • Buffalo
  • Cisco
  • Dell
  • Fujitsu
  • HP
  • 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 practically any device that supports SNMP, the corresponding Management Information Base (MIB) and Object Identifiers (OIDs), and correctly implements the according RFCs. The standard SNMP libraries of PRTG include predefined, common values for the generic SNMP sensors so that you can easily get started with monitoring via SNMP. 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 Simple Network Management Protocol (SNMP).

  • It shows the 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 Simple Network Management Protocol (SNMP).

It 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 hardware component of a server via Simple Network Management Protocol (SNMP).

It shows 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 Simple Network Management Protocol (SNMP).

It 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 Simple Network Management Protocol (SNMP).

It 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 Simple Network Management Protocol (SNMP). You can create it on an SNMP compatible device that provides traffic data via RMON. Depending on the data returned by your device, traffic data for each port can be displayed in different channels, allowing detailed analysis. If available, the sensor queries 64-bit counters.

For each port, the sensor can show, for example:

  • Transmitted kbit/s
  • Packets (#/s)
  • Broadcast Packets (#/s)
  • Multicast Packets (#/s)
  • 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 a device is running via Simple Network Management Protocol (SNMP).

  • It reads the system uptime value of the monitored device and shows it.

SNMP Traffic sensor

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

It 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.

It shows 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
  • 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 Simple Network Management Protocol (SNMP).

It shows 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 Simple Network Management Protocol (SNMP).

It shows the following:

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

SNMP Linux Meminfo sensor

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

It shows 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 input/output (I/O) on disks of a Linux/Unix system using Simple Network Management Protocol (SNMP).

It shows 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 Simple Network Management Protocol (SNMP).

  • It shows the operating status of the monitored service.

Custom SNMP Sensors

For your more individual needs, PRTG offers custom SNMP sensors. The monitoring capabilities of these sensors go beyond the scope of the generic sensors. The custom sensors allow you to show certain values that are not included in the standard libraries of PRTG. With these sensor types, you can monitor most devices that support SNMP and that PRTG does not have native sensor types for. Basically, you just need to find out the required Object Identifiers (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 Simple Network Management Protocol (SNMP).

  • This sensor shows a single numerical value (int64) for a given OID. Each OID always refers to a specific parameter of a certain SNMP device.

Value types include the expected numeric type of the results at the given OID: You can choose between

  • 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-cameraSee this video tutorial SNMP Custom and Library Sensor on our website for more information.

SNMP Custom Advanced sensor

The SNMP Custom Advanced sensor monitors numerical values returned for Object Identifiers (OIDs) using Simple Network Management Protocol (SNMP).

  • The sensor displays numerical values for given OIDs that refer to this specific SNMP device. Up to 10 OIDs and corresponding numerical values are possible.

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 will be able to 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 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.

This sensor shows the following:

  • Response time of the monitored device
  • Optionally a value extracted from the string
  • In the sensor message, the sensor shows the string you search for and which is 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 or you can use a regular expression 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 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 manual section SNMP Custom String Lookup Sensor—Example.

  • This sensor shows 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 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.

  • It can show 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 allows you to 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) library file to create sensors that monitor a device via Simple Network Management Protocol (SNMP). This approach provides custom monitoring beyond the standard SNMP sensors of PRTG.

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

The SNMP Library sensor will automatically create the following custom SNMP sensor types based on the data types available in the MIB:

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

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 file to the Paessler oidlib format, and import it into PRTG. To make setting up your monitoring  as convenient as possible, PRTG comes with pre-compiled oidlib library files that already contain the OIDs of SNMP counters for the most common devices in a network.

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

Default OIDLIB Files Overview

The following files are included in PRTG and are ready to use with the SNMP Library sensor. These allow the extension of your SNMP monitoring to many devices. Please be aware that not all devices and/or parameters may be supported by the libraries.

  • 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, etc.
  • 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, etc.
  • 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, etc.
  • 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, BMC, chassis, COO, cooling, event log, firmware, IDE, keyboard, memory, port, network, processor, SCSI, system, temperature, USB, UUID, etc.
  • 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?