In this book, we learned about DNS principles, resolver configuration, and configuration of various name servers. You must have realized that domain registration and delegation is altogether quite easy. However, in spite of its comprehensibility, the DNS is often a source of problems to ordinary computer users.

The correct diagnosis of computer problems is similar to a correct medical diagnosis. In both cases, it is important not only to reach the correct diagnosis, but also to do so in the minimum time. We can suspect mistakes in a DNS configuration if a user complains either that his or her computer does not communicate at all or, more often, the communication seems to be slow from time to time even if the network infrastructure is fast.

In such cases, if a user asks you for help, you should sit down in front of the user’s computer, run the command prompt (never mind if it is a UNIX or a Windows machine), and find out the following: