Ideally, the total responses should match the total queries. Significant differences between the two can

indicate that the DNS server is not able to handle the current workload.

The rate of recursive queries successfully handled by the DNS server

The ratio of recursive queries to total queries indicates the number of queries that required the DNS server to communicate with other DNS servers to resolve the client requests.

The rate of recursive queries that could not be resolved by the DNS server

Query failures can happen due to various reasons - e.g., requests from clients to invalid domain names/IP addresses, failure in the external network link thereby preventing a DNS server from communicating with other DNS servers on the Internet, failure of a specific DNS server to which a DNS server is forwarding all its requests, etc. A small percentage of failures is to be expected in any production environment. If a significant percentage of failures are happening, this could result in application failures due to DNS errors.

Timeouts can happen because of a poor external link preventing a DNS server from communicating with others. In some cases, improper/invalid domain name resolution requests can also result in timeouts. DNS timeouts can adversely affect application performance and must be monitored continuously.

The number of zone transfer requests received by a DNS server in the last measurement period

Zone transfers are resource intensive. Moreover, zone transfers to anauthorized clients can make an IT environment vulnerable to security attacks. Hence, it is important to monitor the number of zone transfer requests and responses on a periodic basis.

The number of zone transfers that were not serviced by the DNS server in the last measurement period

Zone transfers may fail either because the DNS server does not have resources, or the request is not valid, or the client requesting the transfer is not authorized to receive the results.