Change:
query domain name's canonicalized form.  That is, if a client queries example.com, the ESNI Resource Record might be: <del> Servers MUST ensure that if multiple A or AAAA records are returned for a domain with ESNI support, all the servers pointed to by those records are able to handle the keys returned as part of an ESNI record for that domain. Clients obtain these records by querying DNS for ESNI-enabled server domains.  Clients may initiate these queries in parallel alongside normal A or AAAA queries, and SHOULD block TLS handshakes until they complete, perhaps by timing out. In cases where the domain of the A or AAAA records being resolved do not match the SNI Server Name, such as when RFC7838 Section 2.3 is being used, the SNI domain should be used for querying the ESNI record. Servers operating in Split Mode SHOULD have DNS configured to return the same A (or AAAA) record for all ESNI-enabled servers they service.  This yields an anonymity set of cardinality equal to the number of ESNI-enabled server domains supported by a given client- facing server.  Thus, even with SNI encryption, an attacker which can enumerate the set of ESNI-enabled domains supported by a client- facing server can guess the correct SNI with probability at least 1/ K, where K is the size of this ESNI-enabled server anonymity set. This probability may be increased via traffic analysis or other mechanisms. </del> The "checksum" field provides protection against transmission errors, including those caused by intermediaries such as a DNS proxy running on a home router.

Discussion:
This change does the following: Add support for mandatory extensions, which are those that clients must process else reject the ESNIKeys record. Add a mandatory extension carrying a set of v4/v6 addresses, which is effectively the combined record mode. Add text describing how clients ought to resolve ESNI and A/AAAA records, and use the results to initiate TLS connections.
That's fair. However, it seems to be the price to get this sort of simplicity. Moreover, as an extension, it's not pressed upon all clients for all providers. Also true! I'm hoping that folks who are in the position and capable of vending these records can comment on this design's cost.
Given that there was no serious objection to this change and that it works for at least one operator, I'm merging this PR. We can continue to iterate on as needed in parallel.
issues and advocate for the removal of the _esni prefix. A significant side effect of that is that it becomes impossible to use a CNAME at the apex of a zone in order to refer to ESNIKeys of a server operated elsewhere. Inlining keys, as is often done with A/AAAA at the apex, is not plausible due to key rotation. The issue can largely be mitigated with the introduction of an inclusion mechanism directly in the TXT/ESNI record.
This should be fixed by and follow up changes. Closing as such. Please reopen if necessary!
I don't believe resolves this. 136 effectively requires the address and ESNI information to be stapled together (which I still find objectionable). The issue here is that the apex cannot use a CNAME to delegate to the actual third party provider's ESNI record.. typically it just includes an A/AAAA record at the apex and hopes the pointer doesn't go stale. That's bad enough for A/AAAA but it would be terrible for ESNI because it means copying keying information and hoping it doesn't go stale between two different entities. NAME can you reopen?
Sure! Sorry for the misunderstanding. We can probably update this PR to make use of the new DNS-specific extensions.
Fixed by .
This is a substantial step in the right direction, but the fact that A/AAAA records are basically ignored makes me uneasy. The fact that A/AAAA results are essentially fully embedded would imply that all logic involved in selectively returning those responses has to be duplicated for ESNIKeys, which is also sub-optimal.