Here are some proposed text changes, per Warren's invitation to send text: In section 1.2, change:
2. TargetName: The domain name of either the alias target (for AliasMode) or the alternative endpoint (for ServiceMode). to: 2. TargetName: Either the domain name of the alias target (for AliasMode) or the host name of the alternative endpoint (for ServiceMode). In section 2.4.2, change: As legacy clients will not know to use this record, service operators will likely need to retain fallback AAAA and A records alongside this SVCB record, although in a common case the target of the SVCB record might offer better performance, and therefore would be preferable for clients implementing this specification to use. to: As legacy clients will not know to use this record, service operators will likely need to retain fallback AAAA and A records at the service name, although in a common case the target of the SVCB record might offer better performance, and therefore would be preferable for clients implementing this specification to use. In section 2.4.3, change: In ServiceMode, the TargetName and SvcParams within each resource record associate an alternative endpoint for the service with its connection parameters. to: In ServiceMode, the TargetName and SvcParams within each resource record associate an alternative endpoint for the service with its connection parameters. The TargetName MUST be a host name (as defined in [DNSTerm].) In section 3, the following changes are proposed; they introduce a new term LASTNAME to be used to disambiguate the $QNAME reference so as to remove ATTRLEAF prefixes from the appended target: 1. Let $QNAME be the service name plus appropriate prefixes for the scheme (see Section 2.3). becomes: 1. Let $QNAME be the service name plus appropriate prefixes for the scheme (see Section 2.3). Let $LASTNAME be the service name without any prefixes. 3. If an AliasMode SVCB record is returned for $QNAME (after following CNAMEs as normal), set $QNAME to its TargetName (without additional prefixes) and loop back to step 2, subject to chain length limits and loop detection heuristics (see Section 3.1). becomes: 3. If an AliasMode SVCB record is returned for $QNAME (after following CNAMEs as normal), set $QNAME to its TargetName (without additional prefixes), set $LASTNAME to this new $QNAME and loop back to step 2, subject to chain length limits and loop detection heuristics (see Section 3.1). Once SVCB resolution has concluded, whether successful or not, SVCB- optional clients SHALL append to the priority list an endpoint consisting of the final value of $QNAME, the authority endpoint's port number, and no SvcParams. (This endpoint will be attempted before falling back to non-SVCB connection modes. This ensures that SVCB-optional clients will make use of an AliasMode record whose TargetName has A and/or AAAA records but no SVCB records.) becomes: Once SVCB resolution has concluded, whether successful or not, SVCB- optional clients SHALL append to the priority list an endpoint consisting of the final value of $LASTNAME, the authority endpoint's port number, and no SvcParams. (This endpoint will be attempted before falling back to non-SVCB connection modes. This ensures that SVCB-optional clients will make use of an AliasMode record whose TargetName has A and/or AAAA records but no SVCB records.) If the client is SVCB-optional, and connecting using this list of endpoints has failed, the client now attempts to use non-SVCB connection modes. becomes: If the client is SVCB-optional, and connecting using this list of endpoints has failed, the client MAY attempt to use non-SVCB connection modes, using the origin name (without prefixes), the authority endpoint's port number, and no SvcParams. One additional suggested addition to the end of section 3.1 is: If DNS responses are cryptographically protected, and at least one HTTPS AliasMode record has been received successfully, clients MAY apply Section 9.5 (HSTS equivalent) restrictions even when reverting to non-SVCB connection modes. Clients also MAY treat resolution or connection failures subsequent to the initial cryptographically protected AliasMode record as fatal. [Brian's note: this last would provide some guidance to implementers of clients: a signed HTTPS AliasMode record is a strong signal that the DNS operator is discouraging fallback, albeit at a "MAY" level.] NB: The 2.4.3 change could be removed as it is mostly independent, as could the last addition to 3.1. The 1.2 change is very minor, is not too important but presents a succinct clarification on the hostname vs domain name thing. The 2.4.2 change and section 3 changes together are fixes for the prefix/no-prefix issue (which was basically a scrivener's error, and does not change the semantics at all.) They should stay or go as one unit. Brian On Tue, Aug 30, 2022 at 12:08 AM Brian Dickson < brian.peter.dick...@gmail.com> wrote: > > > On Sat, Aug 27, 2022 at 3:00 PM Ben Schwartz <bem...@google.com> wrote: > >> >> >> On Fri, Aug 26, 2022 at 10:49 PM Brian Dickson < >> brian.peter.dick...@gmail.com> wrote: >> >>> >>> Fail fast may not be appealing, but in some (probably the majority of) >>> cases, it may be the most correct option. >>> >>> It may also be the case that the zone owner knows whether this is the >>> case. >>> I think it is much more likely that explicitly declaring the situation >>> (if known) is more useful than having several billion clients independently >>> attempting to infer whether the first option will even work, let alone >>> provide a useful alternative to the second or third. >>> >> >> In fact, there is one way for the zone owner to disable fallback: enable >> ECH. Fallback is not compatible with ECH, so ECH-aware clients will >> disable fallback when the ServiceMode records contain ECH. >> >> > Wait, what? > > This whole discussion was raised from the perspective of zone owners > publishing AliasMode apex records. > Those owners would not be operating the CDN, which is the whole point of > using a CNAME or AliasMode. > I.e., the zone owner would be the one wanting to disable fallback, but > would not be in a position to do what you suggest. > > The domain's contents are served via a CDN, where the CDN requires > delegation of control, most often with CNAME (or AliasMode at the apex). > The ServiceMode records are placed on the CDN operated zone (in order to > avoid the first connection to establish the AltSvc stuff). > > The AliasMode record cannot be combined with ECH, since no SvcParams are > allowed. The zone owner is not using ServiceMode, that is the declared > assumption. > > If that (ECH) is the only way to disable fallback, that's what the focused > discussion needed to elicit, and I think some slight adjustments are needed > to at least facilitate zone owners preventing fallback. The mechanism > doesn't need to be added to the draft, but likely would get put into a > separate draft or a -bis document. However, there needs to be some daylight > between the fallback method and the mandatory SVCB/HTTPS components, in > order to allow for that development. > > BTW, the concern is less about singleton zone owners than it is about > large scale integrated DNS management of zones in order to accommodate CDN > usage. > > Note also, this issue is not strictly limited to vertical integration > among products/services of the DNS operator; there are large scale > inter-provider (DNS and other services) open partnerships (controlled by > their mutual customers) that have need for the programmatic ability to > assign CDNs and enable/disable fallback (if fallback is part of the > specification). > (For those interested, the not-yet-an-IETF standard for interoperability > between DNS and service providers is Domain Connect. The intent is to > revive the draft for that, which previously lived in the REGEXT WG.) > > I think converting the fallback in the draft into MAY, and having active > discussions, dev, test, and deployment on a voluntary basis outside of the > scope of the current draft, is the fastest path to solving the "no > fallback" signaling issue, and to getting the draft published (with a few > minor tweaks). > > I'll review the other comments, as well as Warren and Viktor's recent > messages, and see if I can come up with some proposed text to make very > limited changes to the draft. > > Brian >
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