> On 17 Apr 2020, at 20:19, Alessandro Ghedini wrote:
>
> Hello,
>
> First off, I have started implementing support for SVCB and HTTPSSVC as part
> of
> the dnspython library [0] and I'd be interested in doing some interop testing
> with other people's implementations.
>
> I also have a few comments/questions about the draft, apologies if they have
> already been discussed in the past (haven't been following the draft from the
> start).
>
> 1. For interop testing purposes it would be very helpful if the draft listed
> commonly agreed upon code-points for the new RR types. Ideally in the form of
> an
> official early assignment from IANA,
Lets wait until we are certain that the format will not change. Every time I’ve
updated the branch there has been a non backwards compatible change.
> but if that's not possible picking a couple
> of codepoints at random from the "private use" range would also be helpful. In
> my implementation I'm currently using "65481" for SVCB and "65482" for
> HTTPSSVC.
BIND’s implementation is available at:
https://gitlab.isc.org/isc-projects/bind9/-/merge_requests/2135
> 2. The structure of the draft is a bit odd, as it lists a bunch of examples
> before introducing any of the records. This was a bit confusing to me, so I'd
> suggest moving sections 1.5 and 1.6 _before_ the examples (that is,
> immediately
> after the introduction). It might also be a good idea to just move the
> examples
> to an Appendix instead.
>
> 3. Would it make sense to move the ESNI/ECHO config paramenter to the
> ESNI/ECHO
> draft instead? This way the DNS draft wouldn't need to depend on the ESNI
> draft
> (so e.g. if ESNI ends up taking longer, this draft could be published without
> having to wait for it).
>
> 4. What is the point of differentiating between AliasForm and ServiceForm?
> Like,
> couldn't the draft just say that the SvcFieldValue is an optional field and be
> done with that? It seems like not having to explicitly differentiate the two
> cases would simplify the draft a bit without sacrificing much, though I might
> be missing something.
>
> 5. Section 2.1.1 says
>
> The presentation format for SvcFieldValue is a whitespace-separated
> list of elements representing a key-value pair, with an absent value
> or "=" indicating an empty value.
>
> It took me longer than I'd like to admit to understand the "with an absent
> value
> or "=" indicating an empty value" part. I'd suggest rewording that paragraph
> to
> something like:
>
> The presentation format for SvcFieldValue is a whitespace-separated list of
> key=value pairs (e.g. "key123=value1 keys456=value2"). When the value, or
> both the value and the "=" are omitted, the value should be interpreted as
> being empty.
>
> Or something better :)
>
> 6. In Section 2.2 it says (in reference to param field values):
>
> o an octet string of the length defined by the previous field.
>
> It might be good to say here that the format of this octet string is defined
> according to the corresponding SvcParamKey, and then reference section 6 for
> ths currently defined keys. The same applies for section 2.1.1 for the
> presentation format.
>
> 7. Section 4.3 says:
>
> All DNS servers SHOULD treat the SvcParam portion of the SVCB RR...
>
> Should it be SvcFieldValue instead of SvcParam? "SvcParam" is not mentioned
> anywhere else.
>
> 8. Maybe I'm missing something, but the following sentence in Section 6.4
> seems
> wrong:
>
> When SvcDomainName is ".", server operators SHOULD NOT include these hints,
> because they are unlikely to convey any performance benefit.
>
> My understanding is that ipv4hint and ipv6hint are the way to solve the ESNI
> multi-CDN problem, so let's say I have "www.example.net" that CNAMEs to both
> "cname.cdn-a.example" and "cname.cdn-b.example". A client queries both A and
> HTTPSVC concurrently for "www.example.net", and receives two answers (the
> answer
> to the A query points to CDN A, while the answer to HTTPSSVC points to CDN B):
>
>www.xample.net 3600 IN CNAME cname.cdn-a.example
>cname.cdn-a.example 3600 IN A 192.0.2.1
>
> and
>
>www.xample.net 3600 IN CNAME cname.cdn-b.example
>cname.cdn-b.example 3600 IN HTTPSSVC 1 . alpn=h3 esniconfig="..."
>
> My understanding is that in this case the client could end up connecting to
> 192.0.2.1 (CDN A) with CDN B's ESNI config (or e.g. with the wrong ALPN). So
> if
> the server doesn't provide IP hints there would indeed be impact on
> performance
> because the client would just straight up fail to connect initially (e.g.
> maybe
> CDN A doesn't support HTTP/3, but CDN B's HTTPSSVC says the client can use it,
> or just because of the wrong ESNI config).
>
> Long story short, I don't think the text should discourage setting ipv4hint
> and
> ipv6hint here. I get that it's SHOULD NOT and not MUST NOT, but it's pretty
> confusing nevertheless.
>
> 9. Speaking of multi-CDN, AFAICT the prob
