Extremely High DNS Data Usage (GBs per Month) My iPhone was using > 2GB a month in data, and 99% of it was due to DNS.  Consistently I was chewing up 50-100MB in data per day.  I would go to Cellular->System Services->DNS and see very little usage elsewhere, but high GB usage for DNS.

What could possibly cause this?  A DNS query is an ipv4 packet or two...

All the other data usage clearly correlated to my actual usage but I could not understand DNS.

This is on an iPhone 8+ that is always updated to the latest iOS within a few days.
Turns out my ad blocker (1Blocker) was the cause.  Once I disabled it, DNS usage flatlined to near zero.  I was chewing up 50-100MB a day in DNS and now it's been a single MB in a week.

Strangely, I have Safari blocked from using cellular.  I often tether another phone's hot spot for use, but that should burn data on that phone and not this one.  Still, 1Blocker burned a ton of data use on this phone.  I don't know if that means it's poorly designed or it was doing something shifty under the covers.