Re: [DNSOP] I-D Action: draft-ietf-dnsop-extended-error-04.txt

[Stephane Bortzmeyer <[e-mail]>]

On Mon, Jan 07, 2019 at 12:30:10PM -0800,
 [e-mail] <[e-mail]> wrote 
 a message of 44 lines which said:

>         Title           : Extended DNS Errors
>         Authors         : Warren Kumari
>                           Evan Hunt
>                           Roy Arends
>                           Wes Hardaker
>                           David C Lawrence
> 	Filename        : draft-ietf-dnsop-extended-error-04.txt

Some remarks but before, note I think that it is very important that
we have a way to report more detailed error causes. One of the biggest
problems of DNSSEC is that there is no easy way for the resolver to
report to the application about a DNSSEC problem. So, the work on this
draft is essential.

Now, the problems:

It seems to me that this draft is mostly for resolvers, most planned
extended codes are useless for authoritative servers (except may be
REFUSED/Lame?).

I suggest to make that clear in the introduction:

These extended error codes are specially useful for resolvers, to
return to stub resolvers or to downstream resolvers. Authoritative
servers MAY use them but most error codes would make no sense for
them.

> Unless a protective transport mechanism (like TSIG [RFC2845] or TLS
> [RFC8094])

Why 8094, which does not have even one implementation, instead of
7858?

> 4.2.3.  SERVFAIL Extended DNS Error Code 3 - Signature Expired
>
>   The resolver attempted to perform DNSSEC validation, but the
>   signature was expired.

I suggest to replace "the signature was expired" by "a signature in
the validation chain was expired".

Rationale: which signature? What if a DS at the parent is sign with an
expired signature?

> 4.2.5.  SERVFAIL Extended DNS Error Code 5 - DNSKEY missing
>
>   A DS record existed at a parent, but no DNSKEY record could be found
>   for the child.

I suggest to replace "no DNSKEY record could be found for the child"
by "no DNSKEY record for this specific key could be found for the
child".

Rationale : the current text seems to imply this code is only when
there is no DNSKEY at all.

> 4.4.1.  NXDOMAIN Extended DNS Error Code 1 - Blocked
>
>   The resolver attempted to perfom a DNS query but the domain is
>   blacklisted due to a security policy.  The R flag should not be set.

The last sentence is touchy. If a stub is configured with two
resolvers, and one is fast but known for lying in some cases that you
disagree with, you may ask a cookie from the other parent (no, resolver).

> 4.4.1.  NXDOMAIN Extended DNS Error Code 1 - Blocked
>
>   The resolver attempted to perfom a DNS query but the domain is
>   blacklisted due to a security policy.

I tend to think it would be a good idea to separate the case where the
policy was decided by the resolver and the case where the policy came
from outside, typically from the local law (see RFC 7725 for a similar
case with HTTP).

Rationale: in the first case (local policy of the resolver), the user
may be interested in talking with the resolver admin if he or she
disagrees with the blocking. In the second case, this would be useless.

Otherwise, I suggest to add an error code:

NOERROR Extended DNS Error Code 3 - Forged answer

   For policy reasons (legal obligation, or malware filtering, for
   instance), an answer was forged.  The R flag should not be set.

Rationale: there is "NXDOMAIN Extended DNS Error Code 1 - Blocked" but
policy-aware resolvers (lying resolvers, in plain english) do not
always forge NXDOMAIN, they can also forge A or AAAA answers.

See also the issue just before, about the need to differentiate
resolver policy from "upper" policy, law, for instance.