Re: [DNSOP] HTTPS/SVCB on Cloudflare DNS

[Mark Andrews <[e-mail]>]

> On 23 Jul 2020, at 19:50, Alessandro Ghedini <[e-mail]> wrote:
> 
> On Fri, Jul 17, 2020 at 10:11:33AM +1000, Mark Andrews wrote:
>> 
>> 
>>> On 17 Jul 2020, at 03:26, Alessandro Ghedini <[e-mail]> wrote:
>>> 
>>> On Fri, Jul 17, 2020 at 01:37:35AM +1000, Mark Andrews wrote:
>>>> Do you have a estimate on when you will enable additional section processing for these records?
>>> 
>>> Not sure I understand the question. Do you mean authoritative servers adding
>>> A/AAAA records to additional section of HTTPS responses?
>>> 
>>> Cheers
>> 
>> Yes.  At the moment there will be lots of redundant queries being made. A, AAAA
>> and HTTPS/SVBC for every level of the chain. If HTTPS/SVBC aware servers actually
>> return A and AAAA records for service form records, we can reduce the number of
>> queries that need to be made.
> 
> I did a little experiment (took me a few days to find the time) with a toy DNS
> server [0]. This is obviously not a proper authoritative server, it's just to
> illustrate the problem.
> 
> When I query the auth server directly I get the HTTPS response as well as the
> additional section records:
> 
>     % dig @ns1.nullroute.dev nullroute.dev. type65
> 
>    ; <<>> DiG 9.16.4-Debian <<>> @ns1.nullroute.dev nullroute.dev. type65
>    ; (1 server found)
>    ;; global options: +cmd
>    ;; Got answer:
>    ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 18948
>    ;; flags: qr rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
>    ;; WARNING: recursion requested but not available
> 
>    ;; QUESTION SECTION:
>    ;nullroute.dev.			IN	TYPE65
> 
>    ;; ANSWER SECTION:
>    nullroute.dev.		300	IN	TYPE65	\# 21 00010000010006026832026833000400042D4D6042
> 
>    ;; ADDITIONAL SECTION:
>    nullroute.dev.		300	IN	A	198.51.100.1
> 
> But if I go through a resolver the additional section seems to be stripped:
> 
>     % dig @8.8.8.8 nullroute.dev. type65 
> 
>    ; <<>> DiG 9.16.4-Debian <<>> @8.8.8.8 nullroute.dev. type65
>    ; (1 server found)
>    ;; global options: +cmd
>    ;; Got answer:
>    ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 62418
>    ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
> 
>    ;; OPT PSEUDOSECTION:
>    ; EDNS: version: 0, flags:; udp: 512
>    ;; QUESTION SECTION:
>    ;nullroute.dev.			IN	TYPE65
> 
>    ;; ANSWER SECTION:
>    nullroute.dev.		299	IN	TYPE65	\# 21 00010000010006026832026833000400042D4D6042
> 
> I tried a few other public resolvers and I see the same. If this is the actual
> behavior of resolvers (rather than just an artifact of my experiment's setup)
> then adding additional section wouldn't seem to provide much benefit for
> "end-user" clients (say, a browser).

I’m trying to determine if you are serious here.  Did you honestly expect recursive
servers that know about HTTPS and SVBC, had hence have code to add the addition section
records to the response, to have been deployed in the 3 weeks since the type codes
have been assigned?  Especially so when parameters like “mandatory” have only appeared
in the latest draft on July 13?  Add to that these records have significantly different
additional section processing to any other type.  It’s not just lookup the type by name
and add it to the additional section which.  It adding CNAMEs, which no other record
requires, and loop prevention code as well. It’s protecting against effectively infinite
chains.

It’s also adding code to detect and these records in responses and decide if they are
appropriate.  Again the rules for doing this differ in design from any other deployed
type.

You can add to all of this, a sense that the records are still not stable and really
should not have had type codes assigned when they where.  There was no stable reference
for “mandatory” when they where assigned.  IANA references draft-ietf-dnsop-svcb-https-00
which doesn’t contain “mandatory”.  The draft was, and potentially still is, not stable
enough for permanent code points.  I’m just hoping that we don’t get into serious
interoperability issues between implementations because of this.  A -00 server can accept
but not verify a record produced by a -01 server over the wire.  A -00 server can’t accept
all records, in presentation form, produced by -01 sources.  Do -01 sources now have to
emit ‘key0=“…”’ for mandatory to work around this incompatibility?  I suspect not as any
-00 servers will be replaced, but there is alway the possibility that someone will come
along and implement HTTPS and SVCB against -00 assuming that the description of the
records there is complete enough (which it clearly isn’t).

> Is the expectation that additional section would help resolvers reduce the
> number of queries rather than the other DNS clients? I guess other clients would
> still need to query A/AAAA and HTTPS in parallel as they don't know whether
> there is an HTTPS record at all.
> 
> In any case we don't have plans right now to implement this on Cloudflare's DNS
> servers, but it's certainly possible. I will discuss this with our DNS people
> and see what they think.
> 
> Cheers
> 
>> We need to get to the state where HTTPS/SVBC alias form always reaches a HTTPS/SVBC
>> service form.  When we are mostly in that state we can stop doing A and AAAA queries
>> along side the HTTPS/SVBC query for names in the HTTPS/SVBC alias form and take the
>> RTT hit on the occasional NODATA response.  To get to that state we need the DNS
>> servers of the content providers to be HTTPS/SVBC aware and to populate the additional
>> section whenever possible.
>> 
>> BIND’s HTTPS/SVBC implementation adds A, AAAA, CNAME, and HTTPS/SVBC records and
>> looks for them in the response.  I would expect all HTTPS/SVBC aware clients to
>> look for these records in the response.  At the moment we don’t look for DNAME in
>> the additional section nor do we add it because, quite frankly, they should not be
>> there in any sensible deployment.  DNAME in the answer section is expected.
>> 
>> Mark
>> 
>>>>> On 17 Jul 2020, at 01:13, Alessandro Ghedini <[e-mail]> wrote:
>>>>> 
>>>>> Hello,
>>>>> 
>>>>> Just a quick note that we have started serving "HTTPS" DNS records from
>>>>> Cloudflare's authoritative DNS servers. Our main use-case right now is
>>>>> advertising HTTP/3 support for those customers that enabled that feature (in
>>>>> addition to using Alt-Svc HTTP headers).
>>>>> 
>>>>> If anyone is interested in trying this out you can query pretty much all domains
>>>>> served by Cloudflare DNS for which we terminate HTTP.
>>>>> 
>>>>> For example:
>>>>> 
>>>>> % dig blog.cloudflare.com type65
>>>>> 
>>>>> ; <<>> DiG 9.16.4-Debian <<>> blog.cloudflare.com type65
>>>>> ;; global options: +cmd
>>>>> ;; Got answer:
>>>>> ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 17291
>>>>> ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
>>>>> 
>>>>> ;; OPT PSEUDOSECTION:
>>>>> ; EDNS: version: 0, flags:; udp: 4096
>>>>> ;; QUESTION SECTION:
>>>>> ;blog.cloudflare.com.		IN	TYPE65
>>>>> 
>>>>> ;; ANSWER SECTION:
>>>>> blog.cloudflare.com.	300	IN	TYPE65	\# 76 000100000100150568332D32390568332D32380568332D3237026832 0004000868121A2E68121B2E00060020260647000000000000000000 68121A2E26064700000000000000000068121B2E
>>>>> 
>>>>> Cheers
>>>>> 
>>>>> _______________________________________________
>>>>> DNSOP mailing list
>>>>> [e-mail]
>>>>> https://www.ietf.org/mailman/listinfo/dnsop
>>>> 
>>>> -- 
>>>> Mark Andrews, ISC
>>>> 1 Seymour St., Dundas Valley, NSW 2117, Australia
>>>> PHONE: [phone]              INTERNET: [e-mail]
>>>> 
>> 
>> -- 
>> Mark Andrews, ISC
>> 1 Seymour St., Dundas Valley, NSW 2117, Australia
>> PHONE: [phone]              INTERNET: [e-mail]

-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: [phone]              INTERNET: [e-mail]