DNS over TLS
|Latest version||RFC 7858, RFC 8310|
May 2016 and March 2018
|Domain Name System|
DNS over TLS (DoT) is a network security protocol for encrypting and wrapping Domain Name System (DNS) queries and answers via the Transport Layer Security (TLS) protocol. The goal of the method is to increase user privacy and security by preventing eavesdropping and manipulation of DNS data via man-in-the-middle attacks.
As of 2020[update], Cloudflare, Quad9, Google, Quadrant Information Security, CleanBrowsing, LibreOps, DNSlify Telsy, AdGuard and Digitalcourage are providing public DNS resolver services via DNS over TLS. BIND users can also provide DNS over TLS by proxying it through stunnel. Unbound has supported DNS over TLS since 22 January 2018. Unwind has supported DoT since 29 January 2019. With Android Pie's support for DNS over TLS, some ad blockers now support using the encrypted protocol as a relatively easy way to access their services versus any of the various work-around methods typically used such as VPNs and proxy servers.
Linux and Windows users can use DNS over TLS as a client through the NLnet Labs stubby daemon or Knot Resolver. Alternatively they may install getdns-utils to use DoT directly with the getdns_query tool. The unbound DNS resolver by NLnet Labs also supports DNS over TLS.
Apple's iOS 14 introduced OS-level support for DNS over TLS (and DNS over HTTPS). iOS does not allow manual configuration of DoT servers, and requires the use of a third-party application to make configuration changes.
systemd-resolved is a Linux-only implementation that can be configured to use DNS over TLS, by editing
/etc/systemd/resolved.conf and enabling the setting
DNSOverTLS. Most major Linux distributions have systemd installed by default.[circular reference]
Nebulo is an open source DNS changer application for Android which supports both DoT and DoH.
In April 2018, Google announced that Android Pie will include support for DNS over TLS, allowing users to set a DNS server phone-wide on both Wi-Fi and mobile connections, an option that was historically only possible on rooted devices. DNSDist, from PowerDNS, also announced support for DNS over TLS in version 1.3.0.
Criticisms and implementation considerations
DoT can impede analysis and monitoring of DNS traffic for cybersecurity purposes. DoT has been used to bypass parental controls which operate at the (unencrypted) standard DNS level; Circle, a parental control router which relies on DNS queries to check domains against a blocklist, blocks DoT by default due to this. However, there are DNS providers that offer filtering and parental controls along with support for both DoT and DoH. In that scenario, DNS queries are checked against block lists once they are received by the provider rather than prior to leaving the user's router.
Encryption by itself does not protect privacy. It only protects against third-party observers. It does not guarantee what the endpoints do with the (then decrypted) data.
DoT clients do not necessarily directly query any authoritative name servers. The client may rely on the DoT server using traditional (port 53 or 853) queries to finally reach authoritative servers. Thus, DoT does not qualify as an end-to-end encrypted protocol, only hop-to-hop encrypted and only if DNS over TLS is used consistently.
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