Troubleshooting Tip: Google DNS with DNS over TLS showing as unreachable

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Description	This article describes the troubleshooting steps and the command that can be used to troubleshoot Google DNS with DNS over TLS showing as unreachable.
Scope	FortiGate 6.2.0 and above.
Solution	DNS over TLS is introduced in FortiOS 6.2.0 and above: DNS over TLS When Google DNS is configured with DoT protocol, the server reachability is showing as Unreachable: Attempt to resolve any domain via FortiGate would fail: It is possible to dump the DNS setting by issuing the command below: diag test app dnsproxy 3 To resolve this issue, it is necessary to change the 'Server hostname' parameter in the DNS configuration: CLI configuration: config system dns     set primary 8.8.8.8     set secondary 8.8.4.4     set protocol dot     set server-hostname "dns.google" end Post changing the server hostname to the Google DNS hostname, DNS resolution would be working as expected: Dump the DNS setting again and it is now possible to see no failure: Related article: Troubleshooting Tip: Using Cloudflare DNS with DNS over TLS showing as unreachable Technical Tip: DNS over TLS (DoT) with 3rd Party Global DNS (Google DNS) Troubleshooting Tip: Quad9 DNS with DNS over TLS showing as unreachable