Re: [Roll] IETF 109 open Questions on P-DAO

"Pascal Thubert (pthubert)" <pthubert@cisco.com> Wed, 25 November 2020 09:28 UTC

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From: "Pascal Thubert (pthubert)" <pthubert@cisco.com>
To: Routing Over Low power and Lossy networks <roll@ietf.org>
Thread-Topic: [Roll] IETF 109 open Questions on P-DAO
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Subject: Re: [Roll] IETF 109 open Questions on P-DAO
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Hello Huimin

> 
> I have a few more questions as following.
> 
> 1. How does the egress know that a local RPL instance is associated with it? For
> example, in non-storing mode, the P-DAO message is sent to the ingress.
 
This is related to the discussion of item 4, and Li's answer to the spun off " Make P-DAO bidirectional [extends] IETF 109 open Questions on P-DAO" thread.

If the route is established with a PDR from the ingress and the ingress is root then the ingress can suggest a TrackID from its pool. 

But without a PDR, how can the root find an available TrackID? 
- Should we have a message from the Root to get one, like a "PDR request" from the root to stimulate a PDR? Or do we expect that there's always a PDR and that the "PDR request" is an external mechanism? 
- Or that the stimulus is an external thing?


> 2. A local RPL instance is rooted at the egress. In fact, it is not a normal RPL since
> there is no RPL maintaining messages such as: DIO, NS, DAO etc.
 
True that there is no DIO since the Root forms the DODAG in memory so DIO is not needed. 
The P-DAO is a DAO, though. If we make the ingress the Root then the storing mode P-DAO does pretty much what a normal DAO does, though it flies over a constrained path as opposed to the one found by DIO.

Take care,

Pascal

> 
> Best regards,
> Huimin
> 
>     Date: Tue, 24 Nov 2020 13:22:04 +0000
>     From: "Pascal Thubert (pthubert)" <pthubert@cisco.com>
>     To: Routing Over Low power and Lossy networks <roll@ietf.org>
>     Subject: [Roll] IETF 109 open Questions on P-DAO
>     Message-ID:
> 
> 	<CO1PR11MB4881B348B4A224DBAEE5BA74D8FB0@CO1PR11MB488
> 1.namprd11.prod.outlook.com>
> 
>     Content-Type: text/plain; charset="us-ascii"
> 
>     Dear all
> 
>     The slides for the P-DAO discussion at IETF 109 are available here:
> 
>     https://datatracker.ietf.org/doc/slides-109-roll-dao-projection/
> 
>     There are a number of open questions that we starting discussing, and would
> need to progress on the list.
>     Some of them were expressed on the list, e.g., from Huimin She. I'd like to
> progress on them all with individual threads.
>     The questions are:
> 
> 
>       1.  Lifetime Unit: could we use a different unit for P-DAO?
>       2.  How to differentiate a P-DAO from a normal DAO in a local instance; new
> flag?
>       3.  Make P-DAO bidirectional?
>       4.  Who sends the PDR? Does it have to be the ingress? If it was egress it
> could propose a TrackId from its namespace. Else could the ingress be the root?
>       5.  Maintaining the sibling state. Should we have text on using RFC 8505
> there?
>       6.  Whether ingress and egress are listed in NPO? Today they are both,
> ingress to indicate the packet source in case of encapsulation and for SRH-6LoRH
> compression reference and egress to build the full SRH-6LoRH. Note that the
> ingress must consume the first entry and use it as source.
>       7.  Track in Track vs. SR Header reload models, see slides
> 
>     Let me open threads to follow up.
> 
>     Keep safe
> 
>     Pascal
> 
> 
> 
> 
> 
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