Thursday, January 23, 2020

FortiGate unreasonable DNS error 53/udp

Hi guys,

having an issue where I experience multiple DNS errors on our FortiGate (v5.4.5) following by a successfull DNS session from same client to the same destination (8.8.8.8 / Google).

This is all happening on the same subnet (Guest-Wifi). Policy basically allows all traffic from that subnet to the Internet without restrictions (any/any). So no Ports blocked here.

Yet the same Policy ID that allows DNS traffic is the same that declines it. Destination Interface/Port is the same and I can't figure out why those drops are happening. Result is that some URLs can't be loaded while others are resolved without any issues.

I've read multiple articles & posts in forums now and the issue seems to be somewhat common but I'm yet to find a solution. Maybe anyone has experienced this before.



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