Data Drain
What is DNS Services, what does it do on iPhone 7, and why does it use so much data? Always at or around the top of my System Services Data Usage record.
iPhone 7, iOS 15
Domain Name Servers (DNS) keep track of which website name belongs to which IP number. A DNS service translates a requested web address into the IP address of the server on which the website runs.
DNS is what takes you to Apple (for update download and others), iCloud (syncing, backup and others), Netflix, YouTube, Google and others.