Telechat Review of draft-ietf-anima-autonomic-control-plane-13

Request Review of draft-ietf-anima-autonomic-control-plane
Requested rev. no specific revision (document currently at 18)
Type Telechat Review
Team Routing Area Directorate (rtgdir)
Deadline 2018-03-05
Requested 2018-02-12
Requested by Alvaro Retana
Other Reviews Secdir Early review of -13 by Liang Xia (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)
Review State Completed
Reviewer Joel Halpern
Review review-ietf-anima-autonomic-control-plane-13-rtgdir-telechat-halpern-2018-03-01
Posted at
Reviewed rev. 13 (document currently at 18)
Review result Ready
Draft last updated 2018-03-01
Review completed: 2018-03-01


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-13
Reviewer: Joel Halpern
Review Date: 1-March-2018
IETF LC End Date: N/A
Intended Status: Proposed Standard

Summary: I have some minor concerns about this document that I think should be resolved before publication.

Major: N/A (Note that three comment is marked *** as they may be more significant.)

    The description of the ACP In the introduction should probably note that the addition of Management capability is beyond the definition provided in section 5 of RFC 7575, and is included to complete the needed set of functionality.

    The definition of data-plane seems to assume that all forwarding (and control?) in all nodes is structured in terms of VRFs.  That seems to overly constrain implementation architecture.  Using VRF to to describe the ACP functionality is a little odd, but likely defnesible.  Declaring that all other functionality is in VRFs seems a step too far.

    The definition of Intent in the terminology section seems to be different from the cited definition in the anima reference model.  "Intent" there seems to refer to a policy language, not an interface.

    It is unclear how the flexible policy defined in section 5 bullet 2 (about which nodes are ACP peer candidates) is consistent with autonomic operation.  It seems that the flexibility is important, so there should be some explanation here about how this is consonant with the stated goals.  I understand that the bootstrap comes from BRSKI, but I do not think that is where the policy comes from?

    The BNF is section 6.1.1 seems to have some oddities.  It may be that none of these can happen for reasons that are described elsewhere, but as written:
  If the local-info is empty, the localpart will be "rfcxxxx." and thus the domain info will be "rfcxxxx.@domain".  Is the period really required in the absence of the local-info
  If the rsub is empty, but the extensions are not empty, it looks like there will be two plus signs (following the optional acp-address) before the first extension.  Is that intended as the way to indicate the absence of the rsub? 
  It also seems odd that the rsub (which is a domain extension) appears in the local-part of the domain information, not in the domain name.  Even though for hashing purposes it is concatenated, with a period, with the domain name. 
 If these oddities are intentional, then there ought to be explanations so the reader is not confused.

    I presume there is not an assumption that all ULA addressed communicating with a node which supports the ACP will be over the ACP.  As I understand it, ULAs may well have other uses outside of ANIMA / the ACP.  Which leads to a question about how the text in 6.1.3 "If the CDP URL uses an IPv6 ULA, the ACP node will try to reach it via the ACP." is expected to be supported?

    The discovery text in section6.3 states that discovery should be run in every physical interface.  Is this intended to be restricted by policy, as described in section 5, bullet 2?

***    The explanation in section 6.5 on channel selection (and security protocol selection) is worded as if the described behavior will lead to reliable interoperation.  The text on why there are limitations (reasonable) doe not explain why mandating dTLS support would not be a reasonable step.   (I hope I missing something, as otherwise this is a major problem rather than being minor.)  It is also hard to align this with the requirements in section 6.7.3. has text about "hop-by-hop reliable retransmission as provided for by TCP".  I am unable to determine what this is saying.

    If I have used section 6.10.3 properly, when the Zone-ID is 0, all nodes within the ULA are within a flat address space.  that does turn the address into an identifier.  It is, as far as I can tell from the description, still a locator in that packets will be routed to the node using the address including the node identifier.  It just means that routing has to work in /127 addresses.  (There is also a reference to "identifier" in  From the usage there, I think that the intention is that this is the generic "name" for the node.  Given that it is routable, it is simply an addresses, not an identifier or a locator.)

    The description in section 6.10 / 6.10.1 / 6.10.2 is about the schema identification is very confusing, and arguably a bad design.  The two schemas use the same schema identifier.  The difference in interpretation is actually provided by the last bit in the upper 64.  If these are the same schema, then it should not need a bit to differentiate them.  They should be explained as a single schema.  Which would presumably result in the Z bit being part of the zone / subnet field.   If they are two different schemas, then move the differentiation to part of the schema identifier (making it 3 bits).  This sort-of different but sort-of the same makes implementation "interesting".  Even if this is extra bit is only needed for schema 00b, it should be in front of the Zone / subnet, not after it.  
    This leads to the obvious observation that either we need two bits, of which we will have 3 settings, and we will use the fourth setting as an extension mechanism if we ever need more formats, or we need at least three bits all the time because we seriously think there will be more formats.

    In section 6.10.5, after stating that it is not even known what the needed usage is for more V values, the document goes on to introduce the complexity of classful nodes numbers, with the leading bit indicating how long the node-number is.  Yes, the rest of the text in that bullet tries to explain why you need both sizes.  It seems like needless complexity that begs for mistakes in implementation.

    In section in describing the prefix lengths, I thought that the point of zone addressing was to allow the use of /64 prefixes.  But it seems here that we will not do so ?

    Section 6.12.5 says "ACP nodes MUST NOT derive their ACP virtual interface IPv6 link local address from their IPv6 link local address used on the underlying interface".  But it does not then seem to provide any advice on what is expected to be used.  Is the loopback ACP supposed to be used somehow?  Or?

    The "configuration" description in 8.2.1 provides a nice description of what information is needed, and what choices are allowed.  It does NOT describe a method for configuring the information.  Please tune the introductory material.

***    Section 10.3.2 paragraph 2 says that devices should change the meaning of "admin down" to mean "down for everything except ACP / Anima".    I can understand why, in an autonomic network, such a state is desirable.  However, that really should be a different state from "admin down".  Operators already understand "admin down" as meaning that this interface will not be used for any traffic.  Changing that is fairly drastic.  "admin limited" or "admin ACP-Only" would seem much better than changing the meaning of "admin down".  The justification in the text seems to be a desire to prevent an operator from doing what he intends.  that seems backwards.  (Note that the distinction between administrative state vs operational state, aka failed, is already well understood.)

***    The notion in 10.3.6 that the device should refuse to disable functionality when an authorized administrator directs such seems flatly wrong.

Editorial / Nits:
    Section 6.3, in talking about DULL GRASP refers to the grasp internet draft.  It refers to section  there is no in the grasp I-D.  As best I can guess the reference should be 2.5.2.

    In the various formats in section 6.10, the lowest bit of the upper 64 bits is mandated to be 0.  Presumably, there is some reason for doing this.  It would be nice to explain it.  

    In section 6.10.5, in the text about how many V values are allowed, the text reads: "2^16 - 65536" which would be 0.  I believe that the intention is "2^16 (i.e. 65536)"

   Section 9.2.2 paragraph 2 begins "Group members must overall the secured".  While I can guess what is intended, I would prefer that were in grammatical English so as to avoid guessing.

    Section 10.5 provides the requirements that were met by choosing RPL for the routing protocol.  Likely RPL is a reasonable choice.  Since this section does not provide comparison or list any alternatives, I would suggest changing "explanation" to "motivation".