Re: [Roll] using the flow label instead of hop by hop

Phil,

The flow label is not protected by any IPSec so it cannot be used as a backchannel end-to-end. Now that would be a hack. 
And it is not for node to node communication but for node to network communication. That, in fact, would be a bad idea when destination options can be used safely.
Over the core internet, 6MAN has specified how the flow label is supposed to be set and it is the responsibility of the root that an outgoing packet.
On incoming packets, a normal host ignores the flow label that it cannot trust anyway. The RPL root will flush it and use it as RPL requires within the RPL domain.

Cheers,

Pascal

-----Original Message-----
From: Philip Levis [mailto:pal@cs.stanford.edu] 
Sent: mardi 23 octobre 2012 17:42
To: Pascal Thubert (pthubert)
Cc: John E Drake; adrian@olddog.co.uk; roll@ietf.org
Subject: Re: [Roll] using the flow label instead of hop by hop

What if an end-host outside the RPL instance wants to use a flow label for its own purposes? It might think that a flow denotes a stream of associated packets to a node within a RPL instance, not the OF that instance happens to use. 

Phil

On Oct 23, 2012, at 4:41 AM, Pascal Thubert (pthubert) wrote:

> Hi:
> 
> <I answered to John from my phone but then realized that I did not 
> copy the list.>
> 
> In short: The packets carried within an instance share a characteristic which the OF optimizes for. 
> The OF determines a RPL topology and thus how the flow that is tagged with that instance is processed in the network. 
> For flows to be processed differently one may different instances.
> 
> Considering how open the definition of flow in 2460 is, this fits. 
> 
> The rank stretches that a bit since it qualifies where the flow is in the Network. 
> Then again RFC 2460 is open enough not to bar anything. 
> 
> Rather, the spirit is for us to do something useful with this field in the forwarding plane and that is exactly what this proposal is doing .
> 
> Cheers,
> 
> Pascal
> 
> 
> -----Original Message-----
> From: John E Drake [mailto:jdrake@juniper.net]
> Sent: lundi 22 octobre 2012 21:15
> To: Pascal Thubert (pthubert); adrian@olddog.co.uk; roll@ietf.org
> Subject: RE: [Roll] using the flow label instead of hop by hop
> 
> Pascal,
> 
> So the information that you are carrying in the IPv6 label field has nothing to do with IPv6 labels?  So, why is this not an egregious hack?
> 
> Yours irrespectively,
> 
> John
> 
> 
>> -----Original Message-----
>> From: roll-bounces@ietf.org [mailto:roll-bounces@ietf.org] On Behalf 
>> Of Pascal Thubert (pthubert)
>> Sent: Saturday, October 20, 2012 2:30 PM
>> To: adrian@olddog.co.uk; roll@ietf.org
>> Subject: Re: [Roll] using the flow label instead of hop by hop
>> 
>> Adrian,
>> 
>> This draft is not mpls. This draft is about carrying the RPL info 
>> (rank, instance, flags) in the flow label as opposed to the HbH which 
>> incurs additional header + eventually tunneling.
>> My other draft on fragment forwarding has a lot more to do with label 
>> switching since the first fragment lays a label that the other 
>> fragments follow. But then we are not using the flow label but a 
>> 6LoWPAN datagram identifier tag.
>> 
>> Cheers,
>> 
>> Pascal
>> 
>> -----Original Message-----
>> From: roll-bounces@ietf.org [mailto:roll-bounces@ietf.org] On Behalf 
>> Of Adrian Farrel
>> Sent: samedi 20 octobre 2012 21:37
>> To: roll@ietf.org
>> Subject: Re: [Roll] using the flow label instead of hop by hop
>> 
>> Speaking as an individual and without an implementation...
>> 
>> Isn't this MPLS?
>> Hasn't the routing area looked at the idea of using the IPv6 flow 
>> label for labelled forwarding more than once in the past?
>> Hasn't the conclusion always been that you could do it, but you would 
>> have to be sure that you were not overloading the field?
>> And hasn't the resulting discussion led to a debate on the value of 
>> label stacks and the impracticality of label stacks using the flow 
>> label?
>> 
>> Cheers,
>> Adrian
>> 
>>> -----Original Message-----
>>> From: roll-bounces@ietf.org [mailto:roll-bounces@ietf.org] On Behalf 
>>> Of Philip Levis
>>> Sent: 20 October 2012 14:50
>>> To: Pascal Thubert (pthubert)
>>> Cc: roll@ietf.org
>>> Subject: Re: [Roll] using the flow label instead of hop by hop
>>> 
>>> On Oct 20, 2012, at 1:19 AM, Pascal Thubert (pthubert) wrote:
>>> 
>>>> Phil;
>>>> 
>>>> There is indeed lot of pressure for this in terms of header sizes 
>>>> and energy
>>> consumption in the *real world*.
>>> 
>>> I'm personally concerned about header sizes and energy consumption 
>>> in The Matrix. Because I don't live in the real world. Oh, wait, 
>>> sorry,
>> I
>>> do. Can you
>> walk
>>> me through the quantitative reasoning that a few bytes of header 
>>> will increase energy consumption? It the belief that it will lead to 
>>> sub-packet
>> fragmentation in
>>> some non-amortized sense? Generally speaking, in low power wireless 
>>> networks, energy consumption is dominated by idle listening and 
>>> communication latency/interval support, not the length of packets.
>>> Of course there is a
>> spectrum
>>> of low power approaches and their point on that spectrum. Are you 
>>> thinking of one in particular?
>>> 
>>> Could implementers who are encountering this pressure comment? I'm a 
>>> sucker for and easily swayed by quantitative data as well as 
>>> first-hand rather than second-hand reports.
>>> 
>>>> And there is no hack in the proposed solution.
>>>> Simply we believe more in practical engineering and ML discussions 
>>>> than we
>>> trust in crystal balls.
>>> 
>>> *coughs politely* I believe in very practical engineering that 
>>> considers long
>> term
>>> consequences. Solving a problem a certain way now might cause 
>>> significant problems in the future. I agree this is a tradeoff -- in 
>>> my personal opinion,
>> nothing
>>> more, the tradeoff on this one is 100% clear.
>>> 
>>> Phil
>>> 
>>> ------
>>> 
>>> Philip Levis
>>> President, Kumu Networks
>>> Associate Professor, Stanford University 
>>> http://csl.stanford.edu/~pal 
>>> _______________________________________________
>>> Roll mailing list
>>> Roll@ietf.org
>>> https://www.ietf.org/mailman/listinfo/roll
>> 
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