Telechat Review of draft-ietf-homenet-front-end-naming-delegation-18
review-ietf-homenet-front-end-naming-delegation-18-dnsdir-telechat-brown-2022-10-17-00

Kia ora, 

I'm a recent addition to dnsdir and have been asked to review this draft - this
is my first formal IETF review, so apologies in advance if I don't quite hit
the right spot in terms of what's looked for here - in particular I'm not sure
how calibrated my "Result" status selection is...

Review Conclusion:

The intent and proposed mechanism the draft seeks to achieve is clear and the
proposed high-level architecture of a hidden master is consistent with the
overall format of the DNS ecosystem.

The proposed implementation of the control channel requires a mode of
communication (mutual TLS authentication via DoT) that is not an existing
standards, nor specified in this document and therefore appear infeasible to me
without further specification taking place.

There are a number of other gramatical nits and improvements in wording which
are needed to improve the clarity and understandability of the standard

Major Issues (aka Not Ready):

Mutual TLS and DoT - 3.2 and 4.6 recommend that the HNA and DM secure their
control channel communications using mutual TLS and DoT - but DoT is not
specified to support mutual authentication. While mutual TLS auth at the
underlying TLS layer is clearly viable - how to integrate that at the DNS
layer, and whether that is compatible with DoT on the existing port, or would
need a further port allocation (and subsequent IANA consideration in 13) would
need to be addressed. None of the alternative future protocols listed in 3.2
support mTLS either as far as I am aware.

Given the recommendation to use XoT (RFC9103) (which does specify mTLS
capability) for the Synchronization channel in 5.1 - I wonder why this protocol
has not also been considered for the control channel instead of DoT? 

As written (recommending DoT with mTLS), I do not believe this standard is
implementable.
 

Minor Issues (aka Ready with Issues):

2 and 3.1: DNSSEC Resolver - is the exclusion of unsigned/non-DNSSEC resolvers
in the terminology and architecture overview intentional? Section 9 confirms
that DNSSEC is not required (only RECOMMENDED), so it is possible that both the
public and internal resolvers being used are not DNSSEC capable - therefore it
seems strange for the architecture overview and terminology to imply that
DNSSEC is required.

3.2: The 4th paragraph begins describing "the main issue", the solution to
which is not explained in the paragraph, or in the referenced Section 4.2
(which is DNSSEC/DS specific vs the NS, A, AAAA context of the paragraph). In
either case, the semantics of how the DM treats the information it receives
from the HNA seems out of place in a section describing and primarily focused
on the mechanics of the communication channel itself. I suggest removing or
rewriting this 4th paragraph to improve the clarity. 

4: I find the format of this section confusing and hard to understand with
sections 4.1-4.4 describing the information to be conveyed, but not how it is
conveyed, and then the message formats being described in 4.5. I suggest it
would be much clearer and more understandable to combine the details in 4.5.x
with the earlier sections (e.g. put the AXFR details from 4.5.1 into 4.1, and
the DNS update details from 4.5.2/4.5.3 into 4.2 and 4.3. 

12: I wonder how protected the HNA actually is and whether more
exploration/discussion of the risks invovled is required here - in an IPv4
use-case, the IP for the services published in the Public Homenet Zone is
highly likely to be the same IP with an open DNS port for the DM to connect to
for XFR, and while the relationship in IPv6 is not as straightforward given the
likely use of privacy addressing, etc it's not particularly hard to scan the
enclosing /64 or beyond for an address with an open DNS port. 

Given the HNA is already opening a control connection to the DM, was
consideration given to re-using that connection (or a 2nd HNA initiated
connection to a different address if there is the need for different servers in
the DM implementation between control/sync channesl) to prevent the need for
opening any listening port on the HNA WAN addresses at all?


Nits (aka Ready with Nits):

1.1: This section is titled Selecting *Names* to Publish, but spends the
majority of its words actually discussing the nuances of which *addresses* to
publish for the selected names. This section may be more accurately and cleary
named to include address selection. 

1.3: There is a missing word (scenarios) in the first sentence which I think
needs to read: "A number of deployment *scenarios* ...

1.3.1: The example would be simpler and clearly if it just stated that the
vendor provisions each device with a TLS key pair and certificate matching the
assigned name which are used for mutual authentication. The current discussion of
'proceeding to authentication' is confusing, as it's not a phrase I've encoutered
before and implies to me that authentication is not completed using the
cert/keys, while the explanation about needing both names/keys for regeneration
seems neither necessary or correct (any trusted key can be used to replace
itself, whether or not a certificate with name is also present). 

1.3.2: I think it would be simpler and clearer if the example focused solely on
establishing trust between DOI/HNA via the provision of credentials and omitted
the speculation about verification of ownership that may or may not be
required, and seems like a very separate concern at a different level of the
stack.

2. Clarification of some definitions

Registered Homenet Domain: Given there can be multiple Public Homenet Zones,
presumably there can also be multiple Registered Homenet Domains which should
be stated here for clarity.

Public Authoritative Servers: s/for the Homenet Domain/for the Registered
Homenet Domain/ - 'Homenet Domain' alone is not a defined term. 

Homenet Reverse Zone: Why is this not called the 'Public Homenet Reverse Zone'?
Given the 'Homenet Zone' is private, and this is considered the reverse for the
'Public Homenet Zone' this seems like a confusing inconsistency. Every other
term starting Homenet refers to an internal resource, while the corresponding
external resources all start with 'Public' except in this case. So I would
expect the Homenet Reverse Zone to be the private zone matching home.arpa
containing RFC1918 and IPv6 ULA addresses, etc. 

3.1: s/detaille din/detailed in/ - in the final sentence of the first paragraph.

3.1: "The DOI is also responsible for ensuring the DS record has been updated
in the parent zone." - This statement is too authoritative, and conflicts with
4.2 which clarifies (correctly) that DS updates in the parent zone are
optional. I suggest removing this statement, or correcting it to somethign like
"Depending on configuration, the DOI may also be responsible...".

3.2: s/RECOMMENDED to use TLS with mutually authentication/RECOMMENDED to use
TLS with mutual authentication/ - in the final sentence of the 2nd paragraph.