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

Toerless Eckert <tte@cs.fau.de> Wed, 24 June 2020 02:35 UTC

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Date: Wed, 24 Jun 2020 04:35:21 +0200
From: Toerless Eckert <tte@cs.fau.de>
To: Joel Halpern <jmh@joelhalpern.com>
Cc: rtg-dir@ietf.org, last-call@ietf.org, draft-ietf-anima-autonomic-control-plane.all@ietf.org, anima@ietf.org, evyncke@cisco.com, rwilton@cisco.com
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Subject: Re: [Anima] Rtgdir last call review of draft-ietf-anima-autonomic-control-plane-24
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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.

http://tools.ietf.org/tools/rfcdiff/rfcdiff.pyht?url1=https://raw.githubusercontent.com/anima-wg/autonomic-control-plane/0caa400fd1c554ece49fddc7dabe8140195aa5bf/draft-ietf-anima-autonomic-control-plane/draft-ietf-anima-autonomic-control-plane.txt&url2=https://raw.githubusercontent.com/anima-wg/autonomic-control-plane/ae9e6cd856ab2706e8b38cc2552f2e77f6b676a5/draft-ietf-anima-autonomic-control-plane/draft-ietf-anima-autonomic-control-plane.txt

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
> ???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.

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 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.

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:

| <8d2d0b06-0982-53a3-0ce0-38a465f58bed@joelhalpern.com>
| 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 6.10.3.1. And that guesswork in 6.10.3.1 was not good, which is
why 6.10.3.1 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 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).

Let me move this here so we can have a cohesive discussion about that section.

>     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.

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, 127.0.0.1, 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 6.10.3.1.  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 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.

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 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.

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 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.

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