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 about the most common reasons for problems when monitoring via SNMP.
Important! Before going any deeper into troubleshooting, you need to have a sound knowledge of the principles and functions of SNMP!
- For a general introduction to the SNMP technology, see Paessler IT Explained: SNMP.
- Find an overview about SNMP, MIBs, and OIDs in How do SNMP, MIBs and OIDs work?
- Find suitable SNMP sensors in What SNMP sensors does PRTG offer?
Basic SNMP Troubleshooting
1. Basic SNMP Requirements for the SNMP Target Device
Ensure the following:
- Enable SNMP on the device. For more details, see How do I install the SNMP service on Windows systems?
- Allow access to SNMP for the machine that is running PRTG Network Monitor in the device’s security settings.
- Allow User Data Protocol (UDP) packages to travel from the machine that is running PRTG to the device you want to monitor and back. If the device and PRTG are on different sides of a firewall, make sure that UDP access to port 161 (SNMP) is allowed. You will also need the return path open. For more information, see the following articles:
- Make sure that the firmware of the monitored device runs at the latest version available! If an SNMP sensor (for example the SNMP Traffic Sensor) does not receive any packets from the monitored device, an update of the firmware of this device might help.
- See also SNMP doesn't work! Can somebody out there please help?! on our Paessler Website.
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/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-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 by allowing the 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!
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 an increased 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 in order 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 Go
- Go to the Paessler SNMP Tester.
- Download the ZIP file and follow the instructions on the page.
- Scan the target device from the system on which your PRTG Probe is running. First scan for uptime, later on for other values, too.
- Check if values are returned.
Refer to the following articles for further information:
- How can I test the functionality of my SNMP device?
- How do I solve "Could not connect" or "Error 10060" messages when using SNMP?
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 log file mibparser.log for debugging purposes of 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 your PRTG installation.
Tips and Tricks
Find more SNMP-related issues in this list:
SNMP, Windows, and PRTG
- How do I install the SNMP service on Windows systems?
- What security aspects must I consider when working with SNMP on Windows?
- I want to use SNMP sensors instead of WMI sensors. What can I do?
- What SNMP Sensors does PRTG offer?
SNMP, Mac OS, and PRTG
SNMP, Linux, and PRTG
SNMP Traps and PRTG
- Is it possible to send SNMP traps using PRTG?
- How can I use the trap receiver of PRTG and what are its limitations?
- How do I test an SNMP Trap Receiver Sensor?
SNMP Sensors and Devices
- How can I see all interfaces when adding an SNMP sensor for my Cisco device?
- Monitoring my Cisco switch doesn't work properly with SNMP. What can I do?
- No Such Name (SNMP error # 2) for NetApp Sensors
- SNMP NetApp System Health: Error 137
- SNMP error # 223 with HP C3000 Blade
- My Juniper switches show false 0 zero values. What can I do?
- What can I check if SNMP and SSH sensors throw timeout and auth errors?
- How can I read “DateAndTime” format OIDs?
- How can I change the defaults for names automatically generated for new SNMP sensors?
- Some of my SNMP sensors do not work after updating from PRTG 8 to PRTG 9 or later (might also work after updates from other versions)
Refer to the following Microsoft TechNet articles for a general introduction to SNMP:
See also the following Paessler White Papers:
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?
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.
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.
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.
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
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.