DNS Private Resolver forwarding ruleset resiliency
We are using DNS Private Resolver for all our tenant's Azure DNS resolution. We have a DNS forwarding ruleset set up that forwards all DNS requests for "ourcompany.com." to 10.0.0.100 (primary onprem DNS server IP) and 10.0.0.200 (secondary onprem DNS server IP). This is all working fine. We have just been looking at the resiliency of this setup. If both IPs were unreachable for five minutes, would the DNS private resolver return any cached DNS results for *.ourcompany.com or would the queries simply fail? If only the primary IP (10.0.0.100) were unavailable, presumably DNS queries would still succeed due to use of the secondary IP, but would there be any noticeable increase in the time to respond to DNS queries as a result?