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Contributor III

FortiGate & SNMP IPsec traffic


we use FortiGate at a lot of customers and monitor everything using PRTG Network Monitor (latest version
I found out today that if I monitor traffic in IPsec site2site tunnels I get strange results.


Here is a concrete example.

FortiGate 100F (6.4.9). There is one IPsec tunnel on the WAN interface to the central FortiGate 200F (6.4.10). All traffic is routed to the IPsec tunnel, nothing passes to the internet directly through the WAN.


This graph is from the WAN interface:


and this graph is from an IPsec tunnel:



As you can see there is a huge difference.

But I am unable to determine when this monitoring problem started. I tried deleting and recreating the problematic sensors but that didn't fix the problem. I also tried using SNMPv3 instead of SNMPv2 and also no luck.

I always considered IPsec tunnels as a classic interface (and that's how the PRTG program also approached it) and it always worked.


Has anyone encountered a similar problem? Other interfaces (physical, vlans or SSL) are displayed correctly via SNMP.


And I also registered that if I view the IPsec tunnel widget on FGT, I only see one direction.widget.png


Thank you.


Contributor II

you are experiencing issues with monitoring IPsec traffic on a FortiGate device using PRTG Network Monitor. Specifically, you are seeing different results when monitoring traffic on the WAN interface versus an IPsec tunnel, and you are unable to determine when the issue started.

Here are some steps you can take to troubleshoot this issue:

1. Verify that the SNMP settings on the FortiGate device are configured correctly. Make sure that SNMP is enabled on the device and that the community string is set correctly.

2. Check that the SNMP sensors in PRTG Network Monitor are configured correctly. Make sure that the sensors are using the correct community string and that they are set up to monitor IPsec traffic correctly.

3. Consider using a different SNMP monitoring tool to see if the issue persists. This may help isolate the issue to PRTG Network Monitor or to the FortiGate device.

4. Check the logs on the FortiGate device for any errors or warnings related to SNMP or IPsec traffic. This may give you more information about what is causing the issue.

5. Consider upgrading the firmware on the FortiGate device to the latest version to see if that resolves the issue. Sometimes firmware updates can address compatibility issues with monitoring tools.

By following these steps, you can further isolate the issue and determine the root cause of the problem. If you are still experiencing issues,

Thanks & Regards,
Faizal Emam
Thanks & Regards,Faizal Emam

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