Code change:
Resolver for any cases in which it would have otherwise used the Unencrypted Resolver.  If the Designated Resolver has a different IP address than the Unencrypted Resolver and the TLS certificate does <del> not cover the Unencrypted Resolver address, the client MUST NOT use the discovered Encrypted Resolver.  Additionally, the client SHOULD suppress any further queries for Designated Resolvers using this Unencrypted Resolver for the length of time indicated by the SVCB record's Time to Live (TTL). </del> <ins> not cover the Unencrypted Resolver address, the client MUST NOT automatically use the discovered Designated Resolver.  Additionally, the client SHOULD suppress any further queries for Designated Resolvers using this Unencrypted Resolver for the length of time indicated by the SVCB record's Time to Live (TTL). </ins> If the Designated Resolver and the Unencrypted Resolver share an IP <del> address, clients MAY choose to opportunistically use the Encrypted </del> <ins> address, clients MAY choose to opportunistically use the Designated </ins> Resolver even without this certificate check (opportunistic). <del> If resolving the name of an Encrypted Resolver from an SVCB record </del> <ins> If resolving the name of a Designated Resolver from an SVCB record </ins> yields an IP address that was not presented in the Additional Answers section or ipv4hint or ipv6hint fields of the original SVCB query, the connection made to that IP address MUST pass the same TLS certificate checks before being allowed to replace a previously known <del> and validated IP address for the same Encrypted Resolver name. </del> <ins> and validated IP address for the same Designated Resolver name. </ins> <del> 4.2. </del> <ins> 4.3. </ins> There are situations where authenticated discovery of encrypted DNS configuration over unencrypted DNS is not possible.  This includes

Related discussion:
text: Right now, we only allow authenticated and matching-IP opportunistic use of the DDR record. While use of the record in a case where authentication fails isn't safe to use automatically, we should clarify that implementations MAY choose to use the information anyhow by policy, and possibly with user control.
For authentication to matter, it generally has to operate without fallback. Currently the text is not very clear on this point, but it sure seems like IP-authenticated mode is expected to fall back to cleartext if no upgrade is possible. I think we need to clarify the use case for an authenticated mode, or abandon the distinction between opportunistic and authenticated. In my view, authenticated mode only makes sense if (1) the resolver is identified by its IP address AND (2) the system knows a priori that this resolver supports encrypted DNS, so that it can refuse to fall back to cleartext if the upgrade information is stripped by a network attacker. This is a sufficiently narrow use case that I lean toward dropping it entirely and recommending Discovery Using Resolver Names (Section 5) or opportunistic instead.
Currently, this is what we say (which I now see a grammatical error in, but there it is): We don't say anything else because that would be out of WG scope. The point of the document is to help a stub resolver configured with a recursive resolver known only by IP address to bootstrap into encrypted DNS. The stub resolver's posture on whether to fall back to unencrypted DNS or simply refuse to use the resolver is its own business. Look at this through a common OS scenario: the OS stub resolver learns an IP address from DHCP, and it's a public IP address (my old ISP did this). It knows of no other resolvers because the user doesn't know what DNS is and that's the default configuration (use network recommendation). If I try to use DDR and I get no answer back, then I'm in the same position as I was before DDR: I know of no other resolver, so I either have to use this one or have no DNS resolutions. DDR did not introduce that conundrum; it offers clients a way out of it when DNR is not present and there is no plain-text DNS attack present. The authenticated DDR mode allows such a client to be confident in the authenticity of the bootstrap even though it started over plain text.