I have a customer who has a FGT 80E with full UTM features. The main web policy has Web Filtering, IPS, AV and SSL inspection Security Profiles assigned. The end users are reporting that randomly they will get redirected to gstatic.com/generate_204. Looking the browser history under gstatic.com/generate_204 it references "Fortinet DNS Service" which made me wonder if it was one of the Security Profiles causing the issue. I removed all profiles from the web rule and the issue still occurred.
I then came across this KB (https://kb.fortinet.com/kb/documentLink.do?externalID=FD36680) regarding QUIC (Quick UDP Internet Connections) and as the customer had reported that the issue was with Google Chrome, I asked them to implement Method 1 from the KB on a machine that was experiencing the issue. Unfortunately this did not resolve the issue.
I have looked at the logs on the FGT and there is nothing there to help me. I am not convinced its a FGT issue (although the reference the Fortinet DNS Service is making me doubt myself) so I am hoping that someone here has seen this before? I have also raised a support ticket with Fortinet in the hope this has been seen before.
The FGT is running firmware v6.4.1 build1637 (GA).
Note: I have seen this error message when dealing with CWPs in the past but this is not applicable in this instance.
Hey there! It sounds like you're dealing with quite the tech mystery. I've encountered similar issues before, and they can be quite frustrating. You've taken the right steps by checking logs and reaching out to Fortinet support. I also suggest you check for some guides at https://www.techtapto.com/what-is-gstatic-why-you-see-it-often/. Keep us updated on how it goes!
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