Subject: [Roll] Non-storing mode comments

From: Matteo Paris <[email-masked]>
Date: Fri, 30 Jul 2010 21:53:43 -0400

Hi,

There are a few places in the draft where I believe the text is 
applicable only for storing mode of operation, and does not make 
sense for non-storing mode.

1.  Section 5: "A RPL Control Message has the scope of a link.  The 
source address is a link local address."  I don't think this is true 
for non-storing DAOs and DAO-ACKs, which are sent multiple hops and 
hence cannot have a link local source address.

2.  Section 5.4.1: "The 'D' flag indicates that the DODAGID field is 
present.  This flag MUST be set when a local RPLInstanceID is used." 
The MUST makes sense for storing mode, where DAOs are sent to 
parents.  But in non-storing mode it is not necessary, because the 
the IP destination of the DAO is the DODAG root, which can be the 
DODAGID since the DODAGID is required to be a routable IPv6 address 
for local instance ids.  We should not require that the DODAGID also 
appear in the DAO in non-storing mode, since in many cases this will 
be redundant.

3. Section 11.2.2.4, Foward Path Recovery, makes sense for storing 
mode, where intermediate routers contain downward state.  However it 
does not make sense for non-storing mode, where intermediate routers 
do not have downward state, and cannot make an alternate forwarding 
decision besides what is indicated in the source routing header of 
the packet.  I think the text should point this out for clarity.

Thanks,
Matteo

---

From: "Pascal Thubert (pthubert)" <[email-masked]>
Date: Sat, 31 Jul 2010 10:50:42 +0200

> 1.  Section 5: "A RPL Control Message has the scope of a link.  The
source
> address is a link local address."  I don't think this is true for
non-storing DAOs
> and DAO-ACKs, which are sent multiple hops and hence cannot have a
link local
> source address.

[Pascal] You are right. 6.4 is very clear that now, non-storing DAO fly
straight to the root along Richard's proposal.
So we need to add that the DAO/ack flow in non-storing is an exception
to the general rule in section 5.

> 2.  Section 5.4.1: "The 'D' flag indicates that the DODAGID field is
present.  This
> flag MUST be set when a local RPLInstanceID is used."
> The MUST makes sense for storing mode, where DAOs are sent to parents.
But
> in non-storing mode it is not necessary, because the the IP
destination of the
> DAO is the DODAG root, which can be the DODAGID since the DODAGID is
> required to be a routable IPv6 address for local instance ids.  We
should not
> require that the DODAGID also appear in the DAO in non-storing mode,
since in
> many cases this will be redundant.
[Pascal] I see what you're saying, but that's also somewhat of a
violation and may have consequences if the method is extended.
I'd rather have a compression algorithm that compresses the option
together with a lot of other stuff, like the prefix of the parent in the
transit option.
Now that the spec has stabilized, it would be good that someone starts
this work.

> 3. Section 11.2.2.4, Foward Path Recovery, makes sense for storing
mode,
> where intermediate routers contain downward state.  However it does
not
> make sense for non-storing mode, where intermediate routers do not
have
> downward state, and cannot make an alternate forwarding decision
besides
> what is indicated in the source routing header of the packet.  I think
the text
> should point this out for clarity.

[Pascal] In non-storing, the 'F' bit is never set. The mechanism is to
fire an ICMP error back to the source.
So clearly, that section does not apply; but I agree it does not hurt to
remind it, as you say, for clarity.

Pascal

---

From: JP Vasseur <[email-masked]>
Date: Sat, 31 Jul 2010 12:04:49 +0200

Just a quick reminder, since we passed WG LC. We'll make sure that  
these two clarifications
get added at some point.

Thanks.

JP

On Jul 31, 2010, at 10:50 AM, Pascal Thubert (pthubert) wrote:

>> parents.
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