[Anima] Rtgdir last call review of draft-ietf-anima-autonomic-control-plane-24

[Joel Halpern via Datatracker <[e-mail]>]

Reviewer: Joel Halpern
Review result: Not Ready

Hello,

I have been selected as the Routing Directorate reviewer for this draft. The
Routing Directorate seeks to review all routing or routing-related drafts as
they pass through IETF last call and IESG review, and sometimes on special
request. The purpose of the review is to provide assistance to the Routing ADs.
For more information about the Routing Directorate, please see
​http://trac.tools.ietf.org/area/rtg/trac/wiki/RtgDir

Although these comments are primarily for the use of the Routing ADs, it would
be helpful if you could consider them along with any other IETF Last Call
comments that you receive, and strive to resolve them through discussion or by
updating the draft.

Document: draft-ietf-anima-autonomic-control-plane-24.txt
Reviewer: Joel Halpern
Review Date: 9-April-2020
IETF LC End Date: N/A
Intended Status: Proposed Standard

Summary:
    I have two major concern about this document that I think should be
    resolved before publication.  The are also a number of minor items that
    warrant attention.

Comments:

While quite long, the draft is significantly improved from earlier versions. 
It does provide significant explanation of its design choices, which is helpful
and appreciated.  Sometimes this seems to end up more as marketing or promotion
instead of explanation, but this is mostly harmless.

In particular, I would like to thank the authors and editors for the addition
of section 9.3 and its careful discussion of the many issues there.

Major Issues:

    Section 6.10.3.1 on the use of Zone-IDs seems, from the material in A.10.1,
    to be dependent upon either configuration (which ACP is supposed to avoid)
    or completely unspecified magic.  Having an addressing and routing scheme
    standardized that is impossible to use seems at variance with appropriate
    practice.  It would be fine to say that provision is made for non-zero
    Zone-IDs in the hope that future work can find ways to scale further using
    this.  But pretending it is well-defined, but not actually defining it,
    seems unacceptable.

    Section 6.12.5.1 on loopback interface is factually wrong.  It conflates
    one particular form of loopback interface with the definition of loopback
    interfaces.  This also leads to the error in the definition section (see
    minor comment below).  (Loopback Interfaces were used long before RFC 4291,
    and on routers were often used for external communication.  This was itself
    a repurposing of the original loopback interface, 127.0.0.1, which was
    indeed for internal use.)

Minor Issues:

   It seems distinctly unfortunate that the definition for Data Plane in
   section 2 explicitly states that this definition is different from that used
   in other work, including other routing work.  This seems a recipe for both
   confusion and mis-communication among technologists.

   In the definition of in-band management in section 2, please remove the
   commentary text on putative fragility.   (I actually agree it has some
   fragility.  The discussion does not belong here.  This is a definition.)  
   The promotional material may be warranted, if jarring, in other parts of the
   documents.  Not in the definitions please.

    The definition of a loopback interface in section 2 is wrong.  It claims
    that loopbacks transmit no external traffic.   They send and receive lots
    of external traffic.  They merely do so by forwarding the traffic
    internally to other interfaces.  The traffic is external.  The particular
    step of the transmission, if implemented naively, is internal.

    If we are going to define ACP as a virtual out of band network, I would
    suggest separating the terms into two definitions.  One for true out  of
    band networks (distinct physical links, switches, and ports), and then a
    definition for virtual out of band network which describes the ACP
    approximation which creates independence from configuration, but not
    independence from the physical links.

    Section 5, bullet 2, talks about a policy as to which peers ACP
    communication should be established.  It would be helpful if this gave a
    reference or indication as to where such policies would come from.  Given
    the emphasis on zero touch, I presume they are not configured on the node? 
    (This issues was in my review of -13.)

    Bullet 4 of section 6.1.3 on checking certificates against the CRL / OCSP
    would seem to be better reworded.  I believe the intended requirements i
    that IF there is ACP connectivity to the CRL / OCSP source, then it should
    be verified.  But that absence of such connectivity should not prevent
    association formation.  (As, if I have read it wright, otherwise we could
    deadlock the startup process.)

    In the example in section 6.5 on Channel selection, in steps 7:C1 and
    11:C2, Node 1 concludes that it is Bob.  However, in steps 12 and 13, the
    text refers to Node1 (Alice).  This seems inconsistent.

    Section 6.7.1 makes an assertion about the lack of need for MTI of security
    mechanisms.  The earlier explanation was well done and seems sound.  This
    shorter one seems wrong, since without MTI there is no good way to know
    what ones neighbors may implement.  I suggest simply removing this text and
    replacing it with a backwards reference to the earlier description.  (The
    rest of the section is useful and clear.)

    In 6.10.3,  ACP Zone Addressing Sub-Scheme, the text claims that when zone
    IDs of 0 are used, the addresses are identifiers, and when non-zero IDs
    aere used, they are locators.  Since in either case the addresses are used
    for packet forwarding, and the addressing information is propagated in the
    routing protocol (RPL), this seems to be a misuse of the locator /
    identifier distinction.  And a misuse for no purpose as the distinction is
    not relevant to the document.  (This odd use of "identifier continues in
    section 6.10.3.1.  Identifier is not a synonym of "flat".  Just say "flat".)

    The assertion about looping packets in the later portion of 6.11.1.1 is
    over-stated.  There are other routing protocols that avoid looping-till-ttl
    without changing the data plane header.  I suggest removing the gratuitous
    comparison with other routing protocols.

    6.12.5.1 refers to the ACP addresses as node addresses.  Technically, the
    IPv6 architecture requires that all addresses are associated with
    interfaces rather than nodes.  I would prefer that this draft not
    needlessly claim to violate that.

    Section 7.2 (L2 DULL GRASP) seems to be doing something quite useful.  I
    think I see how it would work.  The need for some configuration on some
    switches seems inevitable and acceptable.   I think there is one corner
    case that should be avoided, as it seems likely to create significant
    complexity for little or no benefit.  It seems to me that a switch that is
    capable of participating in the ACP should either participate in the ACP on
    all its physical ports, or should not participate in the ACP at all.  I
    would not be surprised if that was the WG intent.  But I could not find the
    text that says this.  (Apologies if it is there and I missed it.)

    Section 9 starts by saying it is informational.  But the first paragraph
    says that some of the content is "necessary" for correct operation.  Thus,
    it seems that some of the content is normative?   (I am not sure, but I
    think the "necessary" material relates to what is needed to be a registrar?)

Nits:
    The second and third paragraphs of section 6.11.1.1 on RPL start with
    duplicated text, and then go on to say different (complementary) things. 
    There is no need for the repetition.

    The rank factor in 6.11.1.6 of 100 megabits as the boundary seems a fairly
    arbitrary choice.  It may be that an arbitrary choice was needed.  Could
    something be said?  In particular, if someone looks at this 5 years from
    now, it may seem quite confusing.