*From:* Colin O'Flynn [mailto:[email protected]]
*Sent:* lundi 12 octobre 2009 18:46
*To:* Julien Abeille (jabeille); '6lowpan'
*Subject:* RE: [6lowpan] Fundamental concerns about 6lowpan ND
Hello,
I understand the problems with 'redesigning' a core IPv6 protocol.
However I'm curious about existing implementations that use full
IPv6 ND, do you have details?
I see the 6LoWPAN ND as a 'necessary evil', however I would love
to
be proven wrong!
Regards,
-Colin
*From:* [email protected] [mailto:[email protected]]
*On Behalf Of *Julien Abeille (jabeille)
*Sent:* October 12, 2009 1:47 PM
*To:* 6lowpan
*Subject:* [6lowpan] Fundamental concerns about 6lowpan ND
Dear WG,
I have serious concerns about the 6lowpan ND draft and would
like to
have the WG opinion on this. I agree that a few issues arise in
lowpan environments, which are mostly linked to the non
transitivity
of some link layers used in lowpans. However, my two major
points of
concern are:
- RFC4861 and RFC4862, which are core to IPv6, are being very
heavily redesigned. I believe that the proposal if it is done in
6lowpan MUST be designed as an optional extension to ND, not a
redesign. The charter states that the draft should propose
"optimizations" and "limited extensions" to ND. It is not the case
at the moment. The proxy ND proposal, the mandatory addressing
model
proposed, also goes beyond the scope of the document as spelled
out
in the charter.
- non transitivity is not a lowpan only issue, hence if
adaptations
to ND must be done, it should be in another WG, probably 6man
If these two points are not respected,
- it questions the applicability of IPv6 in smart object networks:
the draft is redesigning roughly 80% of RFC4861 and RFC4862, which
are core to IPv6
- existing IPv6 implementations will be strongly impacted, as a
number of major components will have to become layer 2 dependant:
-- address resolution will have to be disabled
-- DAD will have to be modified
-- NUD will have to be modified
-- prefix discovery will have to be modified
-- autoconf will have to be modified
-- IPv6 addresses will not be configurable if their IID is not
based
on the MAC address
-- ... all these changes are 6lowpan dependant, as they do not
impact traditional links. This will raise important
interoperability
issues.
- new layer 3 protocol designs will become layer 2 dependant. This
is what is currently happenning in the ROLL WG by proposing to
use a
different message to transport routing information, depending on
the
medium.
Moreover, a number of existing deployments show that the issues
arised on lowpan networks as far as ND is concerned are not huge:
the deployments work, and ND as it is has proven to be power
consumption friendly. DAD is the most problematic procedure, that
requires work, as two hop neighbors do not see NS sent for DAD
(see
at the bottom)
In conclusion, I believe the advantages of rebuilding neighbor
discovery for lowpans are by far inferior to those of keeping
using
the "same IP" on all medium. If some redesign has to be done, it
MUST be done in a more general fashion, probably in 6man, and in a
much lighter way.
Best,
Julien
DAD issue description:
node A and node C see node B, but not each other. nodes A and B
boot, configure a link local address, perfom traditional DAD. It
works. Node C boots with the same MAC address than A, configures
the
same IP address, sends a NS to perform traditional DAD. A does not
see the NS hence C address configuration works. A and C have the
same address. B will not differentiate A and
------------------------------------------------------------------------
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