What is a DNS PTR query?
For reasons of historical irrelevance, a normal DNS query is called an A record. A reverse query is called a PTR (pointer) query. The names A and PTR don’t really mean anything; remember that a lot of such things come about because some engineer created “temporary” names from the top of his head, meaning to change them later, but they sort of just stick around. The thing to remember is that A and PTR queries are unrelated. When you register your domain name (example.com) you go to the owner of .com (Network Solutions) and purchase the address. As part of your registration, you tell Network Solutions something to effect “Please pass any DNS queries for the domain example.com to my DNS server ns1.example.com which is located at the IP address 192.0.2.168”. Thus, when resolving www.example.com, you first ask .com for the DNS server for example.com, which is ns1.example.com/192.0.2.168. You then ask that server for the A record for www. Now going the reverse direction is a bit tougher. Whe
