Re: [Roll] No path DAO problem stmt draft

Cenk Gündogan <> Wed, 02 March 2016 17:31 UTC

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Subject: Re: [Roll] No path DAO problem stmt draft
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Dear Rahul,

I find the problems outlined in your draft very interesting and 

My two cents..

Usually, an implementation has the choice to request acknowledgements 
for DAOs
and I would expect some sort of retry mechanism taking place in case of 
a lost DAO.
I couldn't find any reference to DAO-ACKs in your draft, but I am sure 
that the
stated problems still hold for the DAO <-> DAO-ACK case.
One advantage of having the DAO <-> DAO-ACK case is however, that the 
*knows* whether the NP-DAO reached a previous parent or not.
Unfortunately, there's still the question of how the implementation 
should respond
to such knowledge? Without specifying this somewhere (and I couldn't 
find a reference
in RFC 6550, but I could be wrong), the behaviour is implementation-defined.
This can in turn make the interoperability between different implementations
more difficult.

Would it make sense to widen your proposed draft to also include the
DAO <-> DAO-ACK scenario? And maybe some suggestions about how to
react in such cases?


On 02.03.2016 15:04, Rahul Arvind Jadhav (Rahul Arvind Jadhav, 2012 
Labs) wrote:
> Dear All,
> We recently submitted a draft 
> ( 
> stating problem statements pertaining to No Path DAO messaging in RPL 
> spec.
> The primary pain point that is highlighted is that the No-Path DAO 
> messaging takes a path which has a higher probability of not been 
> available. For e.g. when the node switches its parent, a No-Path DAO 
> is usually generated along the path through the previous parent and 
> the No-Path DAO traverses upwards always along that path. A path which 
> is no longer a preferred path is used for No-Path DAO messaging and 
> thus the probability of No-Path DAO messaging failure is high, 
> resulting in stale routing entries.
> Also there are other negative implications mentioned in the document 
> because of this messaging mode.
> The work drafts the problem statement and explains requirements from 
> solution point of view.
> Kindly feedback if the problem statement impacts you.
> Thanks,
> Rahul
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