Large Scale Measurement on the Adoption of Encrypted DNS

TL;DR

This study measures the adoption and growth of encrypted DNS protocols (DoH, DoT, DoQ) over five months in 2021, revealing stable overall traffic but a significant increase in unknown DoH servers, indicating potential future growth in encrypted DNS usage.

Contribution

It provides the first comprehensive measurement of encrypted DNS adoption trends and introduces a novel method for discovering unknown DoH servers.

Findings

Encrypted DNS traffic remained statistically stationary in early 2021.

The number of unknown DoH servers increased fourfold.

Potential for increased connections to encrypted DNS servers in the future.

Abstract

Several encryption proposals for DNS have been presented since 2016, but their adoption was not comprehensively studied yet. This research measured the current adoption of DoH (DNS over HTTPS), DoT (DNS over TLS), and DoQ (DNS over QUIC) for five months at the beginning of 2021 by three different organizations with global coverage. By comparing the total values, amount of requests per user, and the seasonality of the traffic, it was possible to obtain the current adoption trends. Moreover, we actively scanned the Internet for still-unknown working DoH servers and we compared them with a novel curated list of well-known DoH servers. We conclude that despite growing in 2020, during the first five months of 2021 there was statistically significant evidence that the average amount of Internet traffic for DoH, DoT and DoQ remained stationary. However, we found that the amount of, still unknown and ready to use, DoH servers grew 4 times. These measurements suggest that even though the amount of encrypted DNS is currently not growing, there may probably be more connections soon to those unknown DoH servers for benign and malicious purposes.