Re: [Roll] DCO Invalidation triggered from ancestor node

[Rahul Arvind Jadhav <[e-mail]>]

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]>
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