Subject: [Roll] Comment Section 8.8

From: JP Vasseur <[email-masked]>
Date: Thu, 15 Jul 2010 14:15:53 +0200

8.8.  Storing Mode

    In storing mode, RPL routes messages downward by the IPv6  
destination
    address.  The following rule apply to nodes that are in storing  
mode:

    1.  The Parent Address field of a Transmit Information option MUST  
be
        empty.

    2.  On receiving a unicast DAO, a node MUST compute if the DAO would
        change the set of prefixes that the node itself advertises.  If
        so, the node MUST generate a new DAO and transmit it, following
        the rules in Section 8.4.  Such a change includes receiving a  
No-
        Path DAO.

    3.  When a node generates a new DAO, it SHOULD unicast it to each of
        its DAO parents.  It MUST NOT unicast the DAO to nodes that are
        not DAO parents.

    4.  When a node removes a node from its DAO parent set, it SHOULD
        send a No-Path DAO (Section 5.4.3) to that removed DAO parent to
        invalidate the existing route.

=> Bullet 4. I would suggest a MUST here. Otherwise, this leads to  
potential loops, ... yes we
have mechanisms to clean up, but having a MUST would IMO leads to less  
interop issue.

Thought ?

JP.

---

From: Philip Levis <[email-masked]>
Date: Thu, 15 Jul 2010 10:51:10 -0700

On Jul 15, 2010, at 5:15 AM, JP Vasseur wrote:

> 
> 
> => Bullet 4. I would suggest a MUST here. Otherwise, this leads to potential loops, ... yes we
> have mechanisms to clean up, but having a MUST would IMO leads to less interop issue.
> 
> Thought ?

Given that DAO parents are a subset of DODAG parents, this implies there's a loop in the DODAG. Wouldn't it make more sense to more narrowly define this to the case of moving downward in the DODAG?

Phil

---

From: JP Vasseur <[email-masked]>
Date: Fri, 16 Jul 2010 09:08:19 +0200

Hi,

On Jul 15, 2010, at 7:51 PM, Philip Levis wrote:

> Given that DAO parents are a subset of DODAG parents, this implies  
> there's a loop in the DODAG.

I was referring to two things at the same time:
1) A MUST in the bullet above 4 - as reminder:

4.  When a node removes a node from its DAO parent set, it SHOULD
        send a No-Path DAO (Section 5.4.3) to that removed DAO parent to
        invalidate the existing route.
It should be a MUST here; otherwise the DAO parent may continue to  
send packet to that child

2) And the no-path DOA MUST have its K flag set.

Make sense ?

JP.

> Wouldn't it make more sense to more narrowly define this to the case  
> of moving downward in the DODAG?
>
> Phil

---

From: Philip Levis <[email-masked]>
Date: Fri, 16 Jul 2010 00:12:55 -0700

On Jul 16, 2010, at 12:08 AM, JP Vasseur wrote:

>> Given that DAO parents are a subset of DODAG parents, this implies there's a loop in the DODAG.
> 
> It should be a MUST here; otherwise the DAO parent may continue to send packet to that child
> 

Sort of. The reason why it's a SHOULD and not a MUST is for the case where a node removes another node from its DAO parent set due to the link between them becoming terrible. If the link has failed, you don't want to try send a No-Path DAO along it...

Phil

---

From: JP Vasseur <[email-masked]>
Date: Fri, 16 Jul 2010 09:18:43 +0200

On Jul 16, 2010, at 9:12 AM, Philip Levis wrote:

> Sort of. The reason why it's a SHOULD and not a MUST is for the case  
> where a node removes another node from its DAO parent set due to the  
> link between them becoming terrible. If the link has failed, you  
> don't want to try send a No-Path DAO along it...

If you set K, then this is OK and much better than not let your parent  
know about the issue, right ? Otherwise, why sending the no-DOA in the  
first place.

JP.

---

From: "Pascal Thubert (pthubert)" <[email-masked]>
Date: Fri, 16 Jul 2010 11:54:20 +0200

Hi JP:

This creates a loop if the node moves upwards (reduces its Rank) so it
is good to send a no path. 
If the node does not or fails trying, and if the path is used at all
then datapath validation should discover and fix the issue. 
I think that the "SHOULD" comes with the idea that there are numerous
cases where the path is no more preferred and maintained but still
works.

My proposal is to be specific and make it a MUST in the case of the Rank
reduction that makes the ex parent lower than self, leaving it a SHOULD
or a MAY in the other cases.

Pascal

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On Behalf
Of JP
> Vasseur
> Sent: Friday, July 16, 2010 9:19 AM
> To: Philip Levis
> Cc: ROLL WG
> Subject: Re: [Roll] Comment Section 8.8
> 
> 
> >>>> potential loops, ... yes we have mechanisms to clean up, but
having
> >>>> a MUST would IMO leads to less interop issue.
> >>>>
> >>>> Thought ?
> >>>
don't
> > want to try send a No-Path DAO along it...
> 
know
> about the issue, right ? Otherwise, why sending the no-DOA in the
first place.
> 
> JP.
> 
> >
> > Phil
> 
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