It seems there has already been enhancement request filed on this issue.
CSCzv11808 [Feature Request]: Failover for DNS servers
Latency in web requests when primary DNS server is down
WSA is configured for primary and secondary DNS servers. Primary DNS server is unresponsive and secondary DNS server is responding to web requests
Remove the primary(down) DNS server from the WSA configuration.
Customer wants the DNS servers to fail over to the second DNS server if the primary one is down like what we do for the AD servers. Currently when we have 2 DNS servers configured with priority 0 and priority 1, we try the primary DNS server every time, wait for 5 sec and then switch to the secondary server. If the primary DNS server is down, we still try the same server for each and every connection and slowdown the entire Internet traffic by 5 sec unless we manually remove the primary DNS server. Customer is requesting like a caching/intelligent algorithm where if we see the primary DNS server is non-responsive for like 5 min, then totally ignore this server and start talking to the secondary server right from start. Note: From the CS perspective, I would say close to 50% of the slowness issue reported by customers belongs to this issue.
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