What can I do when my SNMP sensors in PRTG show errors? Are there troubleshooting steps?
Created on Jan 30, 2013 9:25:15 AM by
My SNMP sensors don’t work. What can I do?
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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.
- For a general introduction to the SNMP technology, see Paessler IT Explained: SNMP.
- Find an overview on 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 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 PRTG core server system in the device’s security settings.
- Allow User Data Protocol (UDP) packages to travel from the PRTG core server system to the device that 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 target device runs at the latest version available. If an SNMP sensor (for example, the SNMP Traffic sensor) does not receive any packets from the target 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 website.
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, 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, 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
- Go to the SNMP Tester.
- Download the .zip file and follow the instructions on the page.
- Scan the target device from the probe system. First, scan for uptime, later 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?
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
- 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, macOS, 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?
Other issues
- 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)
More
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
Last change on Jan 3, 2023 8:22:34 AM by
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0
Hello,
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
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.
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