Last Call Review of draft-ietf-anima-autonomic-control-plane-24

Request Review of draft-ietf-anima-autonomic-control-plane
Requested rev. no specific revision (document currently at 30)
Type Last Call Review
Team Routing Area Directorate (rtgdir)
Deadline 2020-04-21
Requested 2020-04-07
Requested by Alvaro Retana
Authors Toerless Eckert, Michael Behringer, Steinthor Bjarnason
Draft last updated 2020-04-09
Completed reviews Secdir Early review of -13 by Liang Xia (diff)
Iotdir Early review of -18 by Pascal Thubert (diff)
Rtgdir Telechat review of -13 by Joel Halpern (diff)
Genart Last Call review of -13 by Elwyn Davies (diff)
Genart Telechat review of -16 by Elwyn Davies (diff)
Secdir Telechat review of -16 by Liang Xia (diff)
Rtgdir Last Call review of -24 by Joel Halpern (diff)
This document had already been reviewed (almost 2 years ago), but it has gone through some changes and is now going through the process again.
Assignment Reviewer Joel Halpern 
State Completed
Review review-ietf-anima-autonomic-control-plane-24-rtgdir-lc-halpern-2020-04-09
Posted at
Reviewed rev. 24 (document currently at 30)
Review result Not Ready
Review completed: 2020-04-09



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 ‚Äč

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

    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.


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 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 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,, 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  Identifier is not a synonym of "flat".  Just say "flat".)

    The assertion about looping packets in the later portion of 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. 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?)

    The second and third paragraphs of section 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 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.