The Swedish Internet Foundation The Swedish Internet Foundation The Swedish Internet Foundation NLnet Labs Sinodun IT This document proposes a mechanism for authoritative DNS servers to signal their support for alternative transport protocols (e.g., DNS over TLS (DoT), DNS over HTTPS (DoH) and DNS over QUIC (DoQ)). This signaling may either be provided within the Additional section of authoritative DNS responses or be the result of direct DNS queries. The former, "opportunistic mode" is hint-based and aims to enable resolvers to discover alternative transports efficiently and then opportunistically upgrade connections to the authoritative, thereby improving privacy, security, and performance for subsequent interactions. The mechanism is designed to not require any protocol change or additional queries. It is safe, backward-compatible, and effective even when DNSSEC validation of the hint is not possible or desired. In certain circumstances and with additional overhead it is also possible to use direct queries to securely obtain authentication information for the authoritative that can then be used to authenticate an encrypted connection. It is also possible to establish a "validated mode" where the communication between the resolver and the authoritative server is provably both secure and authentic. Validated mode may not always be possible, depending on whether the resolver is able to DNSSEC validate the signal or not. When Validated mode is possible it does provide a stronger and more trustworthy connection. This document proposes an improvement to the opportunistic (but blind) testing of alternative transports suggested in RFC9539 by providing a mechanism by which a responding authoritative server may signal what alternative transports it supports. TO BE REMOVED: This document is being collaborated on in Github at: https://github.com/johanix/draft-johani-dnsop-transport-signaling (https://github.com/johanix/draft-johani-dnsop-transport-signaling). The most recent working version of the document, open issues, etc, should all be available there. The authors (gratefully) accept pull requests.