Re: [6lowpan] Fundamental concerns about 6lowpan ND

Adam Dunkels Tue, 13 Oct 2009 10:15:49 -0700

Colin O'Flynn wrote:

Yes, but is Contiki a usable implementation for what we want to do?
How well does sleeping or mesh routing work for instance? That is what Imean by an implementation that uses full ND6 – someone doing mesh +sleeping + RFC4861/2.

Sleeping in Contiki is done with a duty-cycled radio mechanism where theradio is switched off for most of the time and turned on for a fewmilliseconds to check for radio activity. If there is radio activity,the radio is kept on to receive the full packet. To send a packet, thesender sends a string of strobe packets to wake up the receiver. Thistype of mechanism reduces the power consumption (typically to < 1% ofthe radio transceiver power) without affecting the abstraction providedby the link layer: nodes appear to be awake all the time, even if theyspent most of their time sleeping.


/adam

Regards,

  -Colin

*From:* Julien Abeille (jabeille) [mailto:[email protected]]
*Sent:* October 13, 2009 2:23 PM
*To:* Colin O'Flynn; 6lowpan
*Subject:* RE: [6lowpan] Fundamental concerns about 6lowpan ND

Hi Colin,

any stack that passes IPv6 ready tests does, i know two of these, onebeing Contiki/uipv6.

Best,

Julien

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    *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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Adam Dunkels <[email protected]>, +46707731614
http://twitter.com/adunk | http://www.sics.se/~adam/
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Re: [6lowpan] Fundamental concerns about 6lowpan ND

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