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

"Joel M. Halpern" <> Sun, 05 July 2020 01:00 UTC

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To: Toerless Eckert <>
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From: "Joel M. Halpern" <>
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Subject: Re: [Anima] Rtgdir last call review of draft-ietf-anima-autonomic-control-plane-24
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My apologies for the delay in responding to these comments.
The changes seem to nicely address all of my comments.  I hope that I 
will recall this well enough to avoid introducing triple-jeopardy by 
accident.  (Having said that, it appears that my pushing on some of 
these issues a second time contributed to your finding good resolutions 
of the issues.)

On the 7.2 comments, my primary comment was a mistake on my part.  The 
only configuration required is the same configuration that is required 
for ACP nodes, namely turning on ACP.  (Which may or may not be a 
default setting, but is clearly a configurable behavior.)

On the comment about a corner case, I was looking for text saying 
roughly "An L2 node that supports ACP and is enabled to participate 
SHOULD do so on all its L2 interfaces.  I grant this is not a big deal. 
My concern is if the L2 link selection is a partial / proper subset of 
the intended L3 adjacencies, problems could easily result due to traffic 
not arriving at all desired places.

Thank you,

On 6/23/2020 10:35 PM, Toerless Eckert wrote:
> Thanks a lot, Joel
> Personal diff with just the fixes for you, otherwise feel free to compare -25 against
> -25, it has more fixes for Russ Housley and IPsec proto detail enhancements/fixes.
> Cheers
>      toerless
> On Thu, Apr 09, 2020 at 07:16:16PM -0700, Joel Halpern via Datatracker wrote:
>> 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
>> ???
>> 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.
> Any pointers to specific text that sounds to be too marketing wise
> always welcome. Happy to review that. I thought i had eliminated all
> the ones... i did see myself.
>> 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.
> Thank you.
>> 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.
> You brought up this issue in your -13 review and we had a longer thread about
> it which ended in i think this statement of yours:
> | <>
> | My perspective is that I would have preferred to see the system designed such
> | that when Zones are needed, they can be added in a way that does not assume
> | system-wide knowledge of the layout choices.
> |
> | I think you could have achieved that.  I understand that the working group
> | didn't do that.  And beause it is the WG decision, I can live with it.  I wish
> | it were better.
> No protection against double jeopardy in IETF ?
> Maybe its a good thing except for expediency of completion of the draft,
> because i had to rethink the issue again, and while it took a while i
> hope the result is especially good to help with initial ACP adoption
> challenges:
> The included text in the discussion up to -24 is now also in my opinion not very
> useful, it also had technical issues.
> The core issue that was combination of your ask for complete removal
> of the ACP zone address scheme and the (bad) solution of attempting to guess
> at a future way how to provide the final full benefits for the zone address
> scheme in And that guesswork in was not good, which is
> why is now gone in -25.
> [Side note: I think i have the zone solution for a future RFC kinda worked out:
> we would have some manual or autonomic zone edges, grasp announcements within each
> zone announcing the Zone-ID and then nodes with ACP-Zone addresses that
> attach into a zone would update the Zone-ID of their ACP address accordingly.
> E-voila: zone-mobility by updating the zone-id field]
> However, the main disconnect was that this longer term goal alone is not
>   good reason to keep Zone-ID. Instead the main reason to keep it was and is
> the ability to support better partial and incremental adoption of ACP,
> and for that one we do actually have good pre-standard implementation
> experience.
> But i didn't want this in the normative part of the spec, and i either
> didn't get the idea that it could go into the operational part (section 9),
> or i felt such text would be too difficult or too much subject to additional
> review attacks.
> But given how i think it is really an important option for initial
> deployments of ACP in large networks, i finally wrote that, it is
> now a new section 9.4. Pls check it out.
>>      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).
> Let me move this here so we can have a cohesive discussion about that section.
>> 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.
> In practice the term node address is often used, maybe less
> in RFC, but more in practice. And its often done
> interchangably with loopback addresses because without changing
> the actual IPv6 functionality, loopback interfaces are the
> main way to achieve the function operators typically associate
> with a node address.
> Be that as it may, i have tried to end the rewrite of the section
> with a paragraph that is trying to bring the use of the word "Node"
> in-line with the way RFC8402 does it.
>>     (Loopback Interfaces were used long before RFC 4291,
> Yepp, was just bad english to connect something that was meant to be
> read in he context of IPv4 with an example about IPv6.
>>      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.)
> Yepp.
> So, i ended up rewriting the whole section also because EricV asked
> in his review earlier this year if it would not be better to use a new
> term instead of loopback.
> Whe i reviewed existing normaive references it became clear to me that
> loopback is actually a very good logical name for the function we
> need for addresses we want to behave as what non-dogmatic people
> would call a node address. So i hope the explanation in the new
> text for loopback to well justify the naming choice.
> I have also added a bullet list for justifying the loopback address
> use. Really nothing new, but common operational practice, alas, i
> wasn't able to find a list like this in other docs and this
> is an ongoing reason for questions from readers of ACP that do not
> have a background in running IP router networks.
> So hopefully, while this point too took me a lot of time to
> rewrite, it is all for the better.
>> 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.
> Actually, IMHO the term data-plane has always been badly defined in the
> face of the inline-signaling model of IP networks. Are IGP/BGP signaling
> packets data-plane or control-plane ? How about routers connecting via
> L2 unbeknownst to them and their STP packets ? Even if you have an
> opininon, do you have a normative RFC to support your definition ?
> What is the difference between data and forwarding plane ?
> Don't answer... rethoric questions...
> I have replaced two existing paragraphs in the intro with the following
> text that explains the terminology better and shows how in the vision
> of autonomic networks the term is very logical, and that it is just
> existing non-autonomous networks in which there is more to the data-plane
> than what you might expect, but i think that is perfectly fine, especially
> when considering the layering example from above, where one layers (L2, ethernet)
> control and forwarding plane are just considered to be part of a higher layers
> data-plane.
> New text:
> <t>In a fully autonomic network node without legacy control or management functions/protocols, the Data-Plane would be for example just a forwarding plane for "Data" IPv6 packets, aka: packets that are not forwarded by the ACP itself because they are control or management plane packets. In such networks/nodes, there would be no non-autonomous control or non-autonomous management plane. Routing protocols for example would be built inside the ACP as so-called autonomous functions via autonomous service agents, leveraging the ACPs functions instead of implementing them seperately for each protocol: discovery, automaticically established authenticated and encrypted local and distant peer connectivity for control and managemenet traffic and common control/management protocol session and presentation functions.</t>
> <t>When the ACP is added to henceforth so-called non-autonomous nodes that have non-autonomous management plane and/or control plane functions, the ACP instead is best abstracted as a special Virtual Routing and Forwarding (VRF) instance (or virtual router) and the complete pre-existing non-autonomous management and/or control plane is considered to be part of the Data-Plane to avoid introduction of more complex, new terminology only for this case. Like the forwarding plane for "Data" packets, the non-autonomous control and management plane functions can then be managed/used via the ACP. This terminology is consistent with pre-existing documents such as <xref target="RFC8368">"/>.</t>
> <t>In both instances (autonomous and non-autonomous nodes), the ACP is built such that it is operating in the absene of the Data-Plane, and in the case of existing non-autonomous (management, control) components in the Data-Plane also in th
> e presence of any (mis-)configuration thereof.</t>
> /New text
>>     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.
> Ok, i stripped down explanatory text for out-of-band network in terminology
> and instead pimped what you would call "marketing" about it in the introduction section. Easy to find in diff.
> Always happy to get explicit suggestions for how to reduce what you think
> is "jarring". The ability of ACP to even avoid a single case of sending
> out a tech person to a remote site due to misconfigurations is IMHO
> the bigest single use-case benefit in talks with customers, so i think it deserves
> good factual representation and i can not see where the text goes beyond
> that. I am happy if any positive pitching is called "marketing", but
> i definitely do not want anything to be "jarring".
>>      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.
> Fixed.
>>      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.
> Done.
> [ Note: I am btw. not worried about the link-sharing as a career limiting move
>    for ACP, as soon as there is sufficient link redundancy (2 links eliminate 99% of issues).
>    The actual HW design of the nodes to maximize ACP value is more interesting.
>    I had slides about that in a research conference workshop some years back, e.g.: applying
>    concepts such as BMC so that you can use the common HW diag functions
>    you typically expect from OOB support. ]
>>      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.)
> Original -13 thread here:
> | >>      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?
> | >
> | > Would rather not like to add more suggestive text, and thats at best what
> | > i could add. The default policy is the best "autonomic" behavior we know how
> | > to make work: aka: try to connect ACP to all neighbors you can discover. And
> | > we have only defined with DULL GRASP how to find subnet adjacent neighbors.
> | >
> | > The main reason to mention policy is so that there is some leeway to do
> | > more or even (sigh) less than all direct neighbors.
> Double jeopardy ?
> I actually did not bother to fix up the intro section since taking the editor pen
> from Michael. I had kept the "policy" in there as a reminder of Intent to be
> done in the future, but given how we deprioritized
> intent in charter, i felt more happy now than during 13 to fix this.
> Alas, it turns out i also found other points in the overview lacking
> clarity and consistency with the normative sections, so the changes
> here got larger, but hopefully all for the better. Please check.
>>      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.)
> Pls. check the full diff vs. -24 for this, because that fix is in the commit i did for
> Russ Housley before i worked on your review. If you don't like that text either, pls
> suggest better wording, its a bit of a tricky language problem i think, which a native
> speaker might master easier.
>>      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.
> Yikes. How could that have slipped me. Thanks a lot.
>>      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.)
> Done.
>>      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".)
> Hey, i didn't come up with all this confusing an probably wrong understanding
> of locator or identifier, i just fell into the trap of trying to use these terms ;-))
> This is removed now. Hope i found all places. Only locartors left should be
> about GRASP.
> Is there even any agreed upon distinction ? To me, identifier/locator are just
> two roles an address can have based on who is using it for what purpose.
> They're not exclusive to each other IMHO.
>>      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.
> Well... it was IMHO not gratuitous, it was just bad text.
> The intent was not to make the solution sound better than other routing protocols,
> but rather to explain how it is not far worse than other routing protocols given
> the absence of the RPI (RPL Packet Information).
> The text was not good because it only indirectly addressed what
> it intended to describe by just talking about TTL looping. I have replaced this
> paragraph by two paragraphs that hopefully better capture the intent:
> [snip]
>      <t>
>        In RPL profiles where RPL Packet Information (RPI, see <xref target="rpl-Data-Plane"/>)
>        is present, it is also used to trigger reconvergence when misrouted, for example looping, packets
>        are recognized because of their RPI data. This helps to minimize RPL signaling traffic
>        especially in networks without stable topology and slow links.
>      </t>
>      <t>
>        The ACP RPL profile instead relies on quick reconverging the DODAG by
>        recognizing link state change (down/up) and triggering reconvergence signaling
>        as described in <xref target="rpl-dodag-repair"/>.  Since links in the ACP
>        are assumed to be mostly reliable (or have link layer protection against loss)
>        and because there is no stretch according to <xref target="rpl-dodag-repair"/>,
>        loops caused by loss of RPL routing protocol signaling packets should be exceedingly rare.</t>
>      </t>
> [/snip]
> Hope this is an adequate answer to close this point.
> I now have no text about TTL expiry because that is a difficult qualitative
> comparison for which there is IMHO not enough data on evidence: The
> reconvergence with RPL in the ACP profile may be somewhat slower than
> the most common sub-50 msec LFA in SP networks or subsecond SPF-IGP
> fast convergence common in most other networks in scope of ACP ("well manageg,
> aka: private enterprise etc. networks), but the total amount of traffic
> across the ACP will likely be orders of magnitude less than that on the
> Data Plane where the SPF-IGP runs.
> I think convergence with the profile should be 50 msec (link change discovery
> plus O(max-pathlength) * per-node RPL processing latency, but i think
> this is too much analysis for a spec, so no text.
>>      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.
> Hmm.. there is no intent to require configuration. What specifically
> do you think of ?
> The goal is really to support ACP in complete L2-only networks, except that
> the ACP itself is of course L3.
> One core part of the text is explaining how ACP can be supported
> on the most limited L2 hardware where it can work. Aka: withough changing
> the actual L2 HW forwarding, but just by punting GRASP packets so they
> are not flooded by L2.
>>      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.)
> Not sure why you specifically think this is an issue for devices
> operating at L2.
> I have seen all type of weird problems. For example: How do you
> enable autodiscovery of ACP neighbors across the 10Gbps backbone
> interfaces of a router/switch for broadband if those interfaces
> are initially disabled by software because the user is expected
> to first enter an additional license key to use those interfaces....
> Sorry, randomn example. Maybe rephrase your point with an example
> why you think it deserve additional text ? Suggest additional text ?
>>      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 first paragraph does not say "correct operation", and i think
> to remember that i word smithed that paragraph quite
> a bit to walk the thin line: you can not build an ACP without
> understanding this section and follow its advice to
> the extend you deem appropriate or feasible, but we can also not
> normatively standardize what is in this section.
> Some things will hopefully gt standardized via future
> yang model RFC. That stuff is just not standardized beause
> it does not meet the formal bar.
> Most of the stuff is talking about variety of options
> deemed to be necessary or beneficial in various
> situations. Doing even the Yang stuff for the subset
> people will agree to is a lot of work.
> protecting the ACP from operator
> misconfiguration is IMHO necessary. I wouldn't even dare
> to begin guessing what details could get standardized for
> that. Yang models for new interface states would certainly
> be another 5++ year discusion in IETF. better to start
> these things with vendor proprietary Yang models and learn.
> I know from personal experience that you can not successfully
> deploy without humunguous amount of diagnostic as long as
> you have buggy implementations, especially when fitting
> into exising router OS, incurring a lot of unforeseen
> limitations. Very difficult to standardize because its
> all about interaction with the non-autonomic stuff unless
> you can severely isolate ACP in your platform design.
> If you do not understand the discussions about registrars,
> you will have a hard time getting a working support
> backend system for the registars.
> Aka: necessary does not mean standardizable.
>> Nits:
>>      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.
> Right. I reworked the overview to remove duplicates, also structured
> into two subsections to highlight the two key themes of the profile
> (single instance and convergence).
>>      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.
> In german, rule of thumb is called "pi times thumb", obviously much more
> accurate than just thumb ;-)
> I added the following paragraph:
>          <t>This is a simple rank differentiation between typical "low speed"
>          or "IoT" links that commonly max out at 100 Mbps and typical
>          infrastructure links with speeds of 1 Gbps or higher. Given how
>          the path selection for the ACP focusses only on reachability but
>          not on path cost optimization, no attempts at finer grained path
>          optimization are made. </t>
> Heard a nice summary about the new ieee work about the future of 10 Mbps
> ethernet over twisted pair, so i think the cut point at 100 Mbps
> may actually be quite a good one. aka: with just two values i don't
> know how we could do better.
> Aain, thanks a lot for the review.
> Toerless