My IP over DNS
A resolver query reports the client address visible to the DNS service, which can differ from the address configured on the device.
“What is my IP?” is often a web-page task. DNS services from OpenDNS and Google also made it available through a resolver query.
The answer can differ from the address a device expects because it reports the address visible to the resolver. That makes it a useful diagnostic as well as a neat DNS trick.
Primary source: https://www.cambus.net/interesting-dns-hacks/