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.
