Re: [Roll] DCO Invalidation triggered from ancestor node

["Pascal Thubert (pthubert)" <[e-mail]>]

You right Rahul.

I guess nothing prevents it though. Just that you should only report direct parent - child relationships otherwise you may create loops...


Regards,

Pascal

Le 14 mai 2019 à 09:01, Rahul Arvind Jadhav <[e-mail]<mailto:[e-mail]>> a écrit :


I understand that you describe a route redistribution. RPL allows it at your own risk, you need to set the E bit to indicate external.

[RJ] E-bit in 6550 says, “The 'E' flag is set to indicate that the parent router redistributes external targets into the RPL network.  An external Target is a Target that has been learned through an alternate protocol.”
I thought E-bit is used to advertise external prefixes or routes known to 6LR outside RPL domain. Unaware leaves looks like a valid scenario for this but within RPL domain and within the DODAG can a 6LR redistribute routes using this flag?

We use it in the case of unaware leaves. The leaf uses RFC 8505 to talk to the RPL router and the router turns that into a DAO.

Btw the call for adoption for the RPL unaware leaves is out. All support is welcome !
All the best,

Pascal

Le 14 mai 2019 à 07:02, Rahul Arvind Jadhav <[e-mail]<mailto:[e-mail]>> a écrit :
Hello ROLL,

Does RPL allow DAO to be sent unsolicited from a non-target node ? For e.g., can a 6LR node on parent switching use the existing routing state to send DAO on behalf of the childs in sub-dodag to update the routing states on new path ?

This topic came up during rpl-observations discussion in IETF102/103 and it was discussed that it is possible. But I couldn’t find any explicit statements in 6550 allowing this.

I am trying to relate unsolicited DCO proposition with this behavior to understand more.

Thanks,
Rahul


From: Roll [mailto:[e-mail]] On Behalf Of Rahul Arvind Jadhav
Sent: 09 May 2019 17:19
To: Routing Over Low power and Lossy networks <[e-mail]<mailto:[e-mail]>>
Subject: Re: [Roll] DCO Invalidation triggered from ancestor node

Thanks Pascal for the feedback.

The race condition and the associated timer in case of multiple preferred parents is a valid scenario. This scenario needs to be handled regardless of unilateral DCO and is explained explicitly in the draft (Section 4.5.3).

Thanks,
Rahul

From: Roll [mailto:[e-mail]] On Behalf Of Pascal Thubert (pthubert)
Sent: 09 May 2019 17:09
To: Routing Over Low power and Lossy networks <[e-mail]<mailto:[e-mail]>>
Subject: Re: [Roll] DCO Invalidation triggered from ancestor node

Hello Rahul:

It is possible that node D in your picture sends a same DAO (same path seq) via both B and C. An unsolicited DCO sent to upon the first DAO received by B could collision with the DAO via C and create race conditions. E.g. a node destroys a route upon DCO seq 5 and recreates it right after when the DAO same seq 5 comes in. Packets in flight will be sent back with a flag in the RPI or destroyed. Not good.

Note: RPL has a datapath detection for broken routes so if it is effectively being used, the path via C would eventually go away based on the flag above.

So I do not favor unsolicited DCOs, and if done, there should be a timer associated to it to make sure that no DAO comes via C. The duration of that timer is hard to fathom…

All the best,

Pascal

From: Roll <[e-mail]<mailto:[e-mail]>> On Behalf Of Rahul Arvind Jadhav
Sent: mercredi 8 mai 2019 07:07
To: roll <[e-mail]<mailto:[e-mail]>>
Subject: [Roll] DCO Invalidation triggered from ancestor node

Hello ROLL,

During the review of draft-ietf-roll-efficient-npdao-10, there was a point raised by Alvaro which we would like to bring to the WG.

The draft adds DCO msg which allows route invalidation by the common ancestor node. The DCO message is generated by the ancestor node in response to DAO with I-flag (invalidate previous route flag) set in context to the corresponding target. The I-flag is used as a mechanism so that the target is in-charge of its own invalidation. Having said that, the ancestor node has all the state information needed to generate the DCO __unilaterally__.

We would like to understand WG thoughts on “whether this unilateral invalidation from ancestor can be allowed or we should strictly let the ancestor node generate DCO in response to DAO with I-flag set.”

Am not quoting pros/cons of the approaches, because this might bias the thinking and it would be nice to have different perspectives.

A diagram to aid understanding: https://github.com/roll-wg/efficient-route-invalidation/blob/master/unilateral-dco.md

Any feedback will be very useful and appreciated.

Thanks,
Rahul
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