Telechat Review of draft-ietf-roll-rnfd-05
review-ietf-roll-rnfd-05-iotdir-telechat-van-der-stok-2025-02-14-00

This will be a short high-level review, because I am really confused by the
contents; and also my knowledge of RPL is ancient. Below the sources of my
misunderstanding. The network configuration is not clear. The LBR, DODAG root,
usually has at least two interfaces, one wireless LLN interface and a possibly
wired, internet link. Only the LLN seems to be discussed, monitoring the LBR
via the Internet link looks more efficient to me than the proposal of this
document. The fault model of the LLN is unclear, Is it a crash of the LBR CPU
or a failure of the wireless interface. The failure of the wireless interface
can be electronic, but can also be caused by refelections, etc.. The sentinels,
seemingly all the children of the LBR, are supposed to come to an agreement.
The subject of agreement between nodes in a failing communication environment
is discussed in the "Byzantine Generals algorithm", and its many derivatives.
However, no mention is made of this problem and how its known solutions compare
to the solution used here. The document claims many improvements in detecting
LBR failure over the already existing techniques in the RPL network. However,
no numbers are cited as function of the network configuration, for example: a
small network with routes of only two hops, or a large network with many hop
routes. The document seems to claim that removing of routes and reconstructing
routes is no longer needed. I don't understand from the text how that is
possible. One thing strikes me as missing, the standardization of the traffic
patterns provoked by RNFD. It is recommended that "care is taken". That means
ending up with as many traffic patterns as there are manufacturers, possibly
leading to implementations that hinder each other instead of collaborating. I
would expect a number of sending delays and counters with standardized values.