Re: [dns-privacy] John Scudder's No Objection on draft-ietf-dprive-xfr-over-tls-11: (with COMMENT)

Sara Dickinson <sara@sinodun.com> Thu, 06 May 2021 10:13 UTC

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From: Sara Dickinson <sara@sinodun.com>
In-Reply-To: <162015857648.17895.7104332787108510127@ietfa.amsl.com>
Date: Thu, 6 May 2021 11:13:15 +0100
Cc: The IESG <iesg@ietf.org>, draft-ietf-dprive-xfr-over-tls@ietf.org, dprive-chairs@ietf.org, DNS Privacy Working Group <dns-privacy@ietf.org>, tjw.ietf@gmail.com
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Subject: Re: [dns-privacy] John Scudder's No Objection on draft-ietf-dprive-xfr-over-tls-11: (with COMMENT)
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> On 4 May 2021, at 21:02, John Scudder via Datatracker <noreply@ietf.org> wrote:
> 
> John Scudder has entered the following ballot position for
> draft-ietf-dprive-xfr-over-tls-11: No Objection
> 
> When responding, please keep the subject line intact and reply to all
> email addresses included in the To and CC lines. (Feel free to cut this
> introductory paragraph, however.)
> 
> 
> Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html
> for more information about DISCUSS and COMMENT positions.
> 
> 
> The document, along with other ballot positions, can be found here:
> https://datatracker.ietf.org/doc/draft-ietf-dprive-xfr-over-tls/
> 
> 
> 
> ----------------------------------------------------------------------
> COMMENT:
> ----------------------------------------------------------------------
> 
> Thanks for the well-written and easy to follow spec. Below are some comments
> you may want to take into consideration.
> 
> 1. Abstract
> 
>   XFR-over-TLS (XoT).  Additionally, this specification updates
>   RFC1995, RFC5936 and RFC7766.
> 
> Please say a few words about how the spec updates those RFCs, don’t make the
> reader go digging for it.

Propose: 
 "Additionally, this specification updates RFC1995 and RFC5936 with respect to efficient use of TCP connections, and RFC7766 with respect to the recommended number of connections between a client and server for each transport.

> 
> 2. Section 1
> 
>   transfers (this draft) is orthogonal to preventing zone enumeration,
>   though they aim to protect the same information.
> 
> s/this draft/this document/

> 
> 3. Sections 6.1, 6.2
> 
>   3.  If the primary serial is higher than the secondaries serial
> 
> s/secondaries/secondary’s/

> 
> 4. Section 6.3
> 
>   This section attempts to presents a rationale for considering
> 
> “Attempts to present”. But really, why not just “presents”?
> 
> 5. Section 6.3
> 
>   Since the SOA of the published zone can be trivially discovered by
>   simply querying the publicly available authoritative servers leakage
> 
> Comma between “servers” and “leakage”.

Ack to all the above corrections.

> 
> 6. Section 6.3.2
> 
>   For hidden primaries or secondaries the SOA response leaks only the
>   degree of SOA serial number lag of any downstream secondary.
> 
> I don’t understand. This either means the sentence would make sense if only I
> had the right domain knowledge (which is OK then), or it means the sentence
> doesn’t make sense (which isn’t).

Probably better written as:

“For hidden XFR servers (either primaries of secondaries) an SOA response directly from that server only additionally leaks the degree of SOA serial number lag of any downstream secondary of that server.”

Does that help?

> 
> 7. Section 7
> 
>   The following sections include detailed clarifications on the updates
>   to XFR behavior implied in [RFC7766] and how the use of [RFC7828]
>   applies specifically to XFR exchanges.  It also discusses how IXFR
>   and AXFR can reuse the same TCP connection.
> 
> “They also discuss” — agreement in number with “the following sections”.
> 
> 8. Section 7.4
> 
>   This specification for XoT updates the guidance in [RFC7766] to
>   provide the same separation of connection purpose (regular queries
>   and zone transfers) for all transports being used on top of TCP.
> 
> The “for XoT” confuses this sentence, making it sound a bit like the advice is
> restricted to XoT. I think those two words should be struck, it would be just
> fine as “this specification updates…”

Ack to both. 

> 
> 9. Section 8.1
> 
>   For improved security all implementations of this specification MUST
>   use only TLS 1.3 [RFC8446] or later.
> 
> Improved compared to what? I think the first three words could go, then the
> question wouldn’t come up.

Ah - compared to stub to recursive DoT which was specified in 2015 and only required to use TLS 1.2 or later….but I’ll update as suggested

> 
> 9. Section 8.4 (also 10.4)
> 
>   o  the server MUST validate the client is authorized to request or
>      proxy a zone transfer by using one or both of the following:
> 
>      *  an IP based ACL (which can be either per-message or per-
>         connection)
> 
>      *  Mutual TLS (mTLS)
> 
> The former is weaker, surely? I see Martin also raised this in his comments, I
> agree with what he wrote. It’s odd to see these two authorization methods, with
> very different security properties, presented as equivalent with no discussion
> anywhere of their relative (de)merits.

Please see the thread in response to Ben’s DISCUSS on this. 

> 
> 10. Section 8.8.1 (also 8.9.3)
> 
>   The goal of padding AXoT responses would be two fold:
> 
> “Is”, not “would be” (also 893)
> 
> 11. Section 10.2
> 
>   SIG(0) [RFC2931] similarly also provides a mechanism to digitally
> 
> Similarly, or also — pick one.
> 
> 12. Section 11
> 
>   The XoT authentication requirement specified in Section 8.4 addresses
>   the issue of ensuring that the transfers is encrypted between the two
> 
> “Transfers are” or “transfer is”.
> 
> 13. Section 11
> 
>   endpoints directly involved in the current transfers.  The following
>   table summarized the properties of a selection of the mechanisms
> 
> “Summarizes”
> 
> 14. Appendix A
> 
>   For completeness, it is noted that an earlier version of the
>   specification suggested using a XoT specific ALPN to negotiate TLS
> 
> Please define APLN on first use

Yup to all the above. 

> 
> 15. A.4
> 
>   As an aside, whilst [RFC7766] makes a general purpose distinction to
>   clients in the usage of connections (between regular queries and zone
> 
> Do you mean “general purpose distinction between clients“? The use of “to”
> doesn’t make sense to me.

The advice referred to is advice for clients about how many connections they should open. Suggest:

“makes a general purpose distinction in the advice to clients about their usage of connections"

> 
> 16. A.4
> 
>   Client behavior to REFUSED response is not clearly defined (see
>   below).
> 
> I do not see anything relevant below.

Good catch - this text used to be in the body of the document. It should reference section 8.7.

Thanks and regards

Sara.