Re: [Roll] WGLC for draft-thubert-6man-flow-label-for-rpl-03

Robert Cragie <> Wed, 20 August 2014 14:48 UTC

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Date: Wed, 20 Aug 2014 15:48:22 +0100
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Subject: Re: [Roll] WGLC for draft-thubert-6man-flow-label-for-rpl-03
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I have been following this discussion with interest and here is my quick 
take on it:

* Flow label seems a fairly abstract concept and it doesn't seem 
unreasonable to use the space it occupies within a specific domain like 
RPL. What is proposed in draft-thubert-6man-flow-label-for-rpl-03 
doesn't seem consistent with the principle of what a "flow" is though as 
it changes hop-by-hop, which is clearly not the intended purpose for a 
flow label field. However, as others have pointed out, it is still a 
mutable field as far as AH is concerned and therefore that does not 
preclude the use as specified in 
draft-thubert-6man-flow-label-for-rpl-03. It is also clear that the flow 
label has to be reset at the edge of the domain anyway.
* Route-over in a mesh network changes everything. The use of the RPL 
option in RFC6553 does indeed seem reasonable but the IP-in-IP 
construction then complicates matters considerably.
* What Carsten proposes in draft-bormann-6lo-rpl-mesh-01 makes the most 
sense to me as putting it at "layer 2.5" is the logical place to put 
this sort of information due to it being hop-by-hop

So in summary, I have no real objection to what is proposed in 
draft-thubert-6man-flow-label-for-rpl-03 but I think Carsten's approach 
is better.


On 18/08/2014 10:20 PM, Michael Richardson wrote:
> I just want to point out that the RPL Instance ID isn't used for routing
> like the MPLS label. RPL nodes still do longest prefix match routing
> on IPv6 destination address.
> If you had to make an analogy to other technology, it's more like a VLAN
> tag being used to pick a virtual router/routing table.
>> I would prefer to avoid making the trade off if we don't have to. Who knows
>> what future application will use the flow label?
> Yes, my response is: "hi, we are the future. Do you mind if we use that
>       thing you reserved for us?"
>> I'm no RPL expert, but
>> seems more elegant
>> and avoids all of this discussion.
> 6lo-rpl-mesh is certainly merits discussion.
> --
> Michael Richardson <>, Sandelman Software Works
>   -= IPv6 IoT consulting =-
> _______________________________________________
> Roll mailing list