Re: [RTG-DIR] RtgDir review: draft-ietf-6tisch-architecture-21.txt

"Pascal Thubert (pthubert)" <pthubert@cisco.com> Sat, 22 June 2019 16:37 UTC

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From: "Pascal Thubert (pthubert)" <pthubert@cisco.com>
To: "Andrew G. Malis" <agmalis@gmail.com>
CC: "<rtg-ads@ietf.org>" <rtg-ads@ietf.org>, "6tisch-chairs@ietf.org" <6tisch-chairs@ietf.org>, "rtg-dir@ietf.org" <rtg-dir@ietf.org>, "draft-ietf-6tisch-architecture.all@ietf.org" <draft-ietf-6tisch-architecture.all@ietf.org>, "6tisch@ietf.org" <6tisch@ietf.org>
Thread-Topic: RtgDir review: draft-ietf-6tisch-architecture-21.txt
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Date: Sat, 22 Jun 2019 16:37:24 +0000
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Subject: Re: [RTG-DIR] RtgDir review: draft-ietf-6tisch-architecture-21.txt
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Hello Andrew:

This is another change with Gorry’s review.
The spec was intended to follow the path of the DetNet architecture as ses track but we’ll follow the A-Ds and the message was to shoot for informational. So we just changed for it.


Regards,

Pascal

Le 22 juin 2019 à 18:17, Andrew G. Malis <agmalis@gmail.com<mailto:agmalis@gmail.com>> a écrit :

One quick follow-up to my review - I just noticed that while the draft's intended status (in the draft) is Informational, the Datatracker lists it as Proposed Standard. The Datatracker should be updated.

Thanks,
Andy

On Fri, Jun 21, 2019 at 5:28 PM Andrew G. Malis <agmalis@gmail.com<mailto:agmalis@gmail.com>> wrote:
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-6tisch-architecture-21.txt
Reviewer: Andy Malis
Review Date: 21 June 2019
IETF LC End Date: 26 June 2019
Intended Status: Informational

Summary:

I have significant concerns about this document and recommend that the Routing ADs discuss these issues further with the authors.

Overall comments:

For this review, I was asked to "Focus on the impact/implications of the architecture on routing/forwarding." I will leave minor details such as editorial nits to others.

This is a very long and detailed document, and I have no prior experience with IEEE 802.15.4, 6lowpan, 6tisch, RPL, and related technologies. To prepare for this review I did some basic background reading, such an online introduction to IEEE 802.15.4 and RFC 7554. So in this review, I really don't feel competent to comments on some of the more technical aspects related to those technologies. However, I do feel competent to comment from the viewpoint of a naive reader with a general background in routing. As a naive reader, I appreciated the introduction to the technology in sections 1-3.

The primary editor of this draft is also active in the DetNet working group, and leverages the work being done there to support the work in this draft. The draft does reference some DetNet technologies that have not yet been completely specified to the point where they can be implemented such as PREOF (Packet Replication, Elimination and Ordering Functions), although such specifications are an expected deliverable in the DetNet WG. So a full implementation of this architecture may have to wait for the completion of the related DetNet specification work.

With respect to routing and forwarding, this draft builds upon the work already done in the 6lowpan WG, such as RPL for routing and 6lowpan header compression. It adds the necessary scheduling and time synchronization functions needed to support the TSCH aspects of IEEE 802.15.4, which is the point of this work. But other than these new aspects, routing and forwarding should continue to work to the extent that they work in the 6lowpan specifications. My one concern regarding IPv6 forwarding is the use of draft-svshah-tsvwg-lln-diffserv-recommendations in section 4.7.2. See my major issues below for more on this concern.

Major issues:

I'm concerned with the number of references to individual drafts (even if informational) in a major architecture specification, since the rest of the work on this technology, including solution documents, will rest on the correctness and completeness of the architecture. If these references are essential, then I would recommend that publication of the architecture be delayed until it's more clear whether these individual drafts will be adopted by a WG, and any abandoned individual drafts be removed. Otherwise, how can a published architecture depend on unpublished, abandoned work? Speaking of which, I note that one of those referenced drafts, draft-svshah-tsvwg-lln-diffserv-recommendations, hasn't been updated in over four years, and should either be removed or adopted by the 6tisch WG. Another, draft-thubert-bier-replication-elimination, hasn't been updated in over a year. Is it still alive? At least the remaining individual drafts have fairly recent updates.

A related concern is that this draft specifically depends on work to be done elsewhere in and outside of the IETF that is currently unchartered (see section A.2). Many of the individual drafts discussed in the previous paragraph are referenced in this section. To the extent that 6tisch depends on this work for its own eventual success, the WG may wish to evaluate if there are alternative ways to have the necessary work completed, such as using an alternative solution or rechartering the WG to include necessary work that looks unlikely to happen elsewhere.

Minor issue:

To the extent that this architecture makes use of centralized control mechanisms such as PCE, the security considerations should mention this dependency and perhaps have a short discussion of effects on the network if connectivity between the centralized controller and the network nodes is lost, either due to an outage or a deliberate attack, and how such effects could be mitigated.

Thanks,
Andy