External DNS Server Unreachable

Please note that DNS query latency is based on when FGT system DNS sends a query, we will record the time sent. And when a query response is received, the time received will also be recorded. We calculated the latency (weighted 3:7) of the server based on these value.If there is no DNS response packet received or failed, Fortigate shows the status unreachable. Kindly check whether the Fortigate is receiving the DNS response packet from the DNS server. Also the latency value is not updated,if Fortigate do not query the server since there are no transaction of packets.