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Document: draft-ietf-dots-architecture-15
Reviewer: Paul Kyzivat
Review Date: 2020-01-23
IETF LC End Date: 2020-01-27
IESG Telechat date: ?

Summary:

This draft is on the right track but has open issues, described in the 
review.

General:

This is a very well written document! Even though I lack any knowledge 
of the subject domain I was generally able to understand it.

I had trouble classifying some of my issues below. I wanted to make them 
be questions. But in a review such as this it makes more sense to state 
them as issues of clarity in the text, since the reader should ideally 
not be left with questions.

Issues:

Major: 0
Minor: 5
Nits:  0

1) MINOR: Resource Ownership:

The 2nd paragraph of section 2.2.2 stresses that it is important for a 
DOTS Server to verify that the DOTS Client owns the resources over which 
it is requesting mitigation.

There seems to be quite a lot hiding behind that requirement. In 
particular, how is the server supposed to be in a position to do that 
verification? This seems to require that the server have access to 
ownership information. While that may be easy in some cases (e.g., when 
the server is operated by the ISP that assigned the resources to the 
client), in other cases it could be hard. I'd like to see more 
discussion of this.

2) MINOR: Scope and lifetime of sessions:

Section 3.1 states that a session can be a signal channel session or a 
data channel session or both. I'm confused about the relationships here.

If a session can consist of both, how are they related? Is there some 
state that ties them together?

Can a channel survive the loss and reestablishment of a TCP connection? 
Or does the creation of a new connection create a new channel?

What is the act that creates a new channel, and what destroys one?

I'd like to see some more text explaining this.

3) MINOR: Feedback for recursive mitigation:

Section 3.2.3 says:

    ... To maximize
    mitigation visibility to the DOTS client, however, the recursing
    domain SHOULD provide recursed mitigation feedback in signals
    reporting on mitigation status to the DOTS client.  For example, the
    recursing domain's mitigator should incorporate into mitigation
    status messages available metrics such as dropped packet or byte
    counts from the recursed mitigation.

This seems to imply that feedback from So to Cn is routed to Mn for 
merging with Mn's feedback. That seems to violate the architecture. Can 
the feedback from So be routed by Gn back to Cc?

Can this be clarified?

4) MINOR: Security of recursive mitigation:

The last paragraph of section 3.2.3 says:

    Deployment of recursive signaling may result in traffic redirection,
    examination and mitigation extending beyond the initial bilateral
    relationship between DOTS client and DOTS server.  As such, client
    control over the network path of mitigated traffic may be reduced.
    DOTS client operators should be aware of any privacy concerns, and
    work with DOTS server operators employing recursive signaling to
    ensure shared sensitive material is suitably protected.

This sounds like hand waving. Am I right in thinking this is talking 
about incorporating the details of recursion in the service level agreement?

5) MINOR: Normative references:

I was surprised by the scarcity of normative references. I went looking 
for MUSTs referencing RFCs and found three: RFC8612 (DOTS Requirements), 
and RFCs 5389 and 7350 (STUN related). Please consider making these 
normative references.