RNFD: Fast border router crash detection in RPL
draft-ietf-roll-rnfd-07

# Gunter Van de Velde, RTG AD, comments for draft-ietf-roll-rnfd-06

# The line numbers used are rendered from IETF idnits tool: https://author-tools.ietf.org/api/idnits?url=https://www.ietf.org/archive/id/draft-ietf-roll-rnfd-06.txt

# for your convenience, please find some non-blocking COMMENTS

# The idnits tool for draft-ietf-roll-rnfd-06 does give some errors. I assume that these were known to the authors. 


# DISCUSS
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# comments
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7	            RNFD: Fast border router crash detection in RPL

GV> do you want to call this 'crash'? there could be many reasons for a border router to no longer responds. 
Within the document there are many instances of the word crash used.
Would it be correct to say 'failure' instead of crash as a more accurate description?

s/crash/failure/

Gunter Van de Velde
RTG Area Director

"Abstract", paragraph 1
>    By and large, a correct operation of a RPL network requires border
>    routers to be up.  In many applications, it is beneficial for the
>    nodes to detect a crash of a border router as soon as possible to
>    trigger fallback actions.  This document describes RNFD, an extension
>    to RPL that expedites border router failure detection, even by an
>    order of magnitude, by having nodes collaboratively monitor the
>    status of a given border router.  The extension introduces an
>    additional state at each node, a new type of RPL Control Message
>    Options for synchronizing this state among different nodes, and the
>    coordination algorithm itself.


Please expand RPL and RNFD on first use. The expansion of RNFD does not come till Section 1.2.

Section 6, paragraph 1
>    RNFD is largely self-managed, with the exception of protocol
>    activation and deactivation, as well as node role assignment and the
>    related CFRC size adjustment, for which only the aforementioned
>    mechanisms are defined, so as to enable adopting deployment-specific
>    policies.  This section outlines some of the possible policies.

My thanks to Peter Van der Stok for performing an IOTDIR review. Peter points out that the network configuration is not clear. By its own admission, the document accepts that the protocol needs to be activated/deactivated. If there is an assumption that the configuration considerations flow from RFC 6550, Section 18.2, that needs to be called out explicitly. The same is true for monitoring and Section 18.3 of RFC 6550.

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All comments below are about very minor potential issues that you may choose to
address in some way - or ignore - as you see fit. Some were flagged by
automated tools (via https://github.com/larseggert/ietf-reviewtool), so there
will likely be some false positives. There is no need to let me know what you
did with these suggestions.

Section 1, paragraph 2
> des to which the node has links) those ones that are closer to the LBR than t
>                                  ^^^^^^^^^^
In formal contexts, "those" is sufficient.

Section 1.2, paragraph 6
> lled virtual DODAG roots can help tolerating some failures of individual LBRs
>                                   ^^^^^^^^^^
The verb "help" is used with an infinitive.

# Éric Vyncke, INT AD, comments for draft-ietf-roll-rnfd-06
CC @evyncke

Thank you for the work put into this document.

Please find below some non-blocking COMMENT points (but replies would be appreciated even if only for my own education), and one nit.

Special thanks to Michael Richardson for the shepherd's detailed write-up including the WG consensus *but* it lacks the justification of the intended status, especially for such an important update to RPL.

As indicated in the shepherd's write-up, I am puzzled by the lack of email for WGLC even if the history clearly indicates that the WGLC was requested in the datatracker

Other thanks to Peter Van der Stok, the IoT directorate reviewer (at my request), please consider this iot-dir review:
https://datatracker.ietf.org/doc/review-ietf-roll-rnfd-05-iotdir-telechat-van-der-stok-2025-02-14/ (and I have read Konrad's reply)

I hope that this review helps to improve the document,

Regards,

-éric


## DISCUSS (blocking)

As noted in https://www.ietf.org/blog/handling-iesg-ballot-positions/, a DISCUSS ballot is just a request to have a discussion on the following topics:

### 

## COMMENTS (non-blocking)

### Abstract

Same as Mahesh, please expand RNFD in the abstract (and possibly in the title).

s/This document describes RNFD/This document specifies RNFD/

Unsure whether `even by an order of magnitude` should be in the abstract, it is a little 'marketing' ;-)

### Section 1

Please expand RPL at first use.

### Section 3

English is not my primary language but I wonder whether the use of "Therefore" is correct in `LBRs are DODAG roots in RPL, and hence a crash of an LBR is global in that it affects all nodes in the corresponding DODAG. Therefore, each node running RNFD for a given DODAG explicitly tracks the DODAG root’s current condition`

`it must be done by the root’s neighbors` seems to imply that all neighbors are sentinel... suggest using "can only be done".

s/A Sentinel node is *the* DODAG root’s neighbor /A Sentinel node is *a* DODAG root’s neighbor /

I also wonder whether detecting a root crash by its links health is a valid assumption, I could imagine case where the root is not more working to build the DODAG but its links are still up.

### Sections 4.1 & 4.2

At first sight, it seems that the text about the operations (value, zero, ...) is duplicated.

### Section 6.1

No need to reply, but I am slightly concerned that good operations of RNFD relies on some manual configurations and I am unsure whether all LLN can be manually configured.

### Section 6.2

Should this rater be a "MUST" in `it is RECOMMENDED to issue a new DODAG Version` ? I.e., to provide more stability.

## NITS (non-blocking / cosmetic)

### Use of SVG graphics

To make a much nicer HTML rendering, suggest using the aasvg too to generate SVG graphics. It is worth a try ;-)

Thanks for working on this specification. I am balloting no objection but would emphasis to respond to the TSVART review by Mirja, thanks Mirja for a good review. 
That review has similar observations as mine. On top of those observations - I would like to know a bit more about the "Care" part on not to overload the Root. Are we talking about some rate control on the probe or is it about a circuit breaker to stop overloading? We need more guidance here.