As a first step toward encrypting the last portion of internet traffic that has historically been cleartext, we have partnered with Cloudflare DNS on a pilot project. This pilot takes advantage of the benefits of Transport Layer Security (TLS) — a widely adopted and proven mechanism for providing authentication and confidentiality between two parties over an insecure channel — in conjunction with DNS. This solution, DNS over TLS (DoT), would encrypt and authenticate the remaining portion of web traffic.
With this DoT pilot, people browsing Facebook and using Cloudflare DNS enjoy a fully encrypted experience, not just when they connect to Facebook using HTTPS, but also at the DNS level, from their computers to Cloudflare DNS, and from Cloudflare DNS to Facebook name servers. Online security has changed considerably since the late 1980s, when the Domain Name System (DNS) was first standardized to allow connection to entities by the means of simple mnemonic names, such as facebook.com. Many improvements have been made, and a large portion of web traffic is now connected via HTTPS.
But there are still some issues inherent in sending cleartext on the wire.
Source: fb.com