NTP bursts from FortiGate firewalls

(This summarizes a problem mentioned in other discussions.)

A recent enhancement to FortiOS, used in the FortiGate firewall, did not handle NTP DNS changes correctly. When DNS mapping changed FortiGate firewalls sent 10 second duration NTP bursts at rates that could exceed 20,000 requests/second. NTP Pool servers were impacted due to the use of DNS load balancing. Our team monitored three NTP pool servers and detected over 150 FortiGate devices sending NTP bursts.

FortiGate support identified the problem: Bug ID 607015

FortiGate support informed us that FortiOS 6.2.4, released on May 12, 2020, fixed the problem. Operators of the FortiGate firewall must install that software, it is not an automatic upgrade. We don’t know when the updates will be complete. Questions should be directed to FortiGate support.

We recommended that FortiGate apply for a Vendor Zone .

Miroslav Lichvar
Hal Murray
Steve Sommars


Ha, no better than TP-Link.

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The rate of the bursts is different in different zones. From the zones I’m currently monitoring, the US zone seems to be most impacted with about 13% of NTP requests generated by these broken clients. Over time, we should see how quickly are the clients being updated.


Due to unrelated issues FortiOS 6.2.4 adoption has been insignificant. FortiNet now says 6.2.5, slated for mid-August, will be the recommended upgrade. This is disappointing, to say the least.

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