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My SNMP sensors don’t work. What can I do?



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

important prtg snmp troubleshooting

Created on Jan 30, 2013 9:25:15 AM by  Gerald Schoch [Paessler Support]

7 Replies

Accepted Answer



This article applies as of PRTG 22

SNMP and PRTG: Basic troubleshooting

Customers who use PRTG sometimes report issues when they set up monitoring for their systems with 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 notice: Before going any deeper into troubleshooting, we recommend that you familiarize yourself with the principles and functions of SNMP.

Basic SNMP troubleshooting

1. Basic SNMP requirements for the 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 SNMP:

  • SNMP v1
  • SNMP v2c (recommended)
  • SNMP v3

It is important to know which SNMP version you must select, because if it is not supported by the server or device that you want to monitor, you will receive an error message. These provide minimum information only, for example could not connect.

Check or change the SNMP version that is 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.
  • User names
  • Passwords

Error messages that indicate 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 scanning 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 Interval Delay SNMP or Open Requests channel of the 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,, 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, 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 SNMP Tester.
  2. Download the .zip file and follow the instructions on the page.
  3. Scan the target device from the probe system. First, scan for uptime, later 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 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 MIB Importer.

Note: PRTG creates the log file 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, macOS, and PRTG

SNMP, Linux, and PRTG

SNMP traps and PRTG

SNMP sensors and devices

Other issues


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

See also the following Paessler White Paper:

Created on Jan 30, 2013 9:39:00 AM by  Gerald Schoch [Paessler Support]

Last change on Jan 3, 2023 8:22:34 AM by  Brandy Greger [Paessler Support]



Can this be clarified?

"SNMP requires the use of UDP ports >1023 to the PRTG client side. This is important for your firewall settings."

I thought that SNMP used UDP ports 161 and 162? What would I set in my Windows firewall to accommodate the above statement? Would I set the firewall to allow incoming on port 1023? Or is it everything greater than 1023?


Created on Mar 31, 2015 9:30:09 PM




The UPD port 161 is used for snmp and port 162 for SNMP traps. By default on the PRTG Server Windows machine the outgoing Ports >1023 (greater than 1023) are open for snmp. It is not necessary to open incoming requests greater than 1023.

Created on Apr 2, 2015 2:56:38 PM by  [email protected]



This may help you and others with Sophos firewalls, but we had to set the PRTG snmp version to V1. No matter what the Sophos version is, as long as the PRTG server is authorized to the Sophos, then set PRTG to V1. PRTG set to V2c and V3 seemed to balk and give no sensors. After changing to V1, everything lit up.

Right click the device, Edit, Settings, scroll down to Credentials for SNMP, uncheck it and then check that the version is V1. Do an auto discovery on that device and it should find a bunch of stuff for you. Been a year trying to figure this out. Got it from a network guy across the way who was messing around. Hope it helps.

Created on Feb 12, 2016 11:59:47 PM



This may or may not apply to you, but I was running PRTG in Server 2016 on a Hyper-V host connected obviously to a virtual switch that was physically a 6 NIC Team on my Host.

Teaming didn't work so great. Connected the vm to a single network card instead of the team and all my problems went away. Before I would get slow, spotty peformance, maybe 1/10 or at best 3/10 repsonses to my snmp polls.

Now it's rock solid.

If anyone ends up here and is teaming their nics for prtg, I'd suggest against it. Couldn't find any information on this anywhere, so it was a day spent with wireshark and powershell until I figured it out. Not fun.

Created on Sep 11, 2017 9:44:37 PM



This has now been fixed. If you want to keep snmpd running on reboot type: snmp service enable (+port) Then you can manually add snmp users via: snmp user add commands or Go into expert mode: cd /etc/snmp vi snmpd.users.confadd for example: rocommunity SNMPSTRING

Created on Mar 9, 2018 3:30:04 PM

Last change on Mar 9, 2018 3:30:04 PM



Most people have at one time or another experienced a computer problem like the situations just described, and if you haven't, chances are you will at some point. When a problem occurs, don't panic! Instead, work your way through some basic troubleshooting techniques and try to solve the problem.

Created on Apr 30, 2018 5:01:19 PM

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.