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