This article applies as of PRTG 20

What can I do when my SNMP sensors in PRTG show errors? Are there troubleshooting steps?

SNMP and PRTG: Basic troubleshooting

Every so often, customers who use PRTG Network Monitor report issues when they set up monitoring for their systems using Simple Network Management Protocol (SNMP).

In most cases, these issues result from a malfunctioning SNMP configuration or installation.

This article provides an overview on the most common reasons for problems when monitoring via SNMP.

Getting started

Important! Before going any deeper into troubleshooting, you need to have sound knowledge of the principles and functions of SNMP!

Basic SNMP troubleshooting

1. Basic SNMP requirements for the SNMP target device

Ensure the following:

2. PRTG settings for SNMP

Check the following SNMP settings in PRTG:

SNMP connection errors

PRTG supports three versions of the SNMP protocol:

  • SNMP Version 1
  • SNMP Version 2c (recommended)
  • SNMP Version 3

It 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. Unfortunately, these provide minimum information only, for example could not connect.

Check or change the SNMP version used by PRTG in the Settings | Credentials for SNMP Devices of a device or group.

Note: SNMP v1 does not support 64-bit counters, which may result in invalid data when monitoring traffic via SNMP. We recommend that you use SNMP v2c (most common) or SNMP v3.

SNMP authentication errors

Similar error messages occur if the authentication does not match:

  • Community strings: A community string is similar to a user ID or password in that it allows access to a device’s statistics. PRTG sends it along with all SNMP requests. If the community string is incorrect, the device will discard the requests and will not respond. This value is case sensitive!
  • Usernames
  • Passwords

Error messages indicating that something is wrong with these requirements are often:

  • Could not connect
  • Error # 10060
  • Error # 2003

Performance limits with SNMP

SNMP v3 has software-dependent performance limitations due to SSL encryption. If you encounter overload problems with SNMP v3, try the following options:

  • Increase the monitoring interval of the SNMP v3 sensors. Currently, PRTG is able to handle roughly 40 requests per second and computer core, depending on your system. This means that, on a common 1.x GHz computer with two cores, you can monitor about 5,000 SNMP v3 sensors with a 60-second scanning interval.
  • Distribute the SNMP v3 sensors over two or more probes if you experience increased values in the Probe Interval Delay SNMP or Probe Open Requests channel of the Core/Probe Health sensor.
  • Switch to SNMP v1 or v2 if you can go without encryption, because these versions do not have these limitations.

SNMP target device for monitoring

It might not work to query data from a probe device via SNMP (querying localhost, 127.0.0.1, or ::1). In this case, add this device to PRTG with the IP address that it has in your network and create the SNMP sensor on this device.

Detailed SNMP troubleshooting

If you need to troubleshoot your SNMP sensors and have checked all basic SNMP requirements, you can debug SNMP activities to find communication and/or data problems in SNMP monitoring configurations.

For this, Paessler provides a test program, the Paessler SNMP Tester, which runs simple SNMP requests against a device in your network. If the connection works with this tool, it will also work with PRTG.

Debugging SNMP activities—steps to take

  1. Go to the Paessler SNMP Tester.
  2. Download the ZIP file and follow the instructions on the page.
  3. Scan the target device from the system on which your PRTG probe is running. First scan for uptime, later on for other values, too.
  4. Check if values are returned.

Refer to the following articles for further information:

Importing MIBs

Many network devices and programs come with Management Information Base (MIB) files that describe the parameters and readings available for monitoring via SNMP. With the Paessler MIB Importer, you can import these MIB files and convert them into OID libraries for PRTG. This way, you can easily set up SNMP Library sensors. For more information, go to Paessler MIB Importer and Converter.

Note: PRTG creates the logfile mibparser.log for debugging MIB imports. This file contains all warnings and errors that might occur when reading an MIB file. You can find the file in the \MIB subfolder of the PRTG program directory.

Tips and tricks

Find more SNMP-related issues in this list:

SNMP, Windows, and PRTG

SNMP, Mac OS, and PRTG

SNMP, Linux, and PRTG

SNMP traps and PRTG

SNMP sensors and devices

Other issues

Further reading

Refer to the following Microsoft TechNet articles for a general introduction to SNMP:

See also the following Paessler White Papers:




Disclaimer:
The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.