Subject: [6lo] RFC4944 fragmentation reassembly with care of security flag

From: Alexander Aring <[email-masked]>
Date: Tue, 18 Apr 2017 16:21:40 +0200

Hi,

while implement MLE draft for Linux I think I detected some behaviour
which is missing in reassembly part of RFC4944.

MLE has some requirement to 802.15.4 security suite to enable or disable
it for different type of MLE messages. In my case I extended ancillary
data of POSIX sockets for special 802.15.4 attributes (which will maybe
another RFC, but I never wrote one before).

Anyway, I asked myself how the security flag and reassembly of RFC4944
works together. Quote part of RFC4944:

...

 The recipient of link fragments SHALL use (1) the sender's 802.15.4
   source address (or the Originator Address if a Mesh Addressing field
   is present), (2) the destination's 802.15.4 address (or the Final
   Destination address if a Mesh Addressing field is present), (3)
   datagram_size, and (4) datagram_tag to identify all the link
   fragments that belong to a given datagram.

...

and I think somewhere need to be added that ALL fragments ?MUST? be have
the same security flag. It's some logical assumption by me that it
?MUST? check on this.

However the Linux implementation of RFC4944 don't do that currently (I
putted it on my list to fix that) - But maybe this part should be updated
to adding the part that all fragments ?MUST? have the same security flag
on 802.15.4 frame level.

Don't know it really need to have a MUST here, that's why I wrote ?MUST?
:-)

- Alex