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

[Philip Levis <[e-mail]>]

On Nov 5, 2012, at 7:33 AM, Pascal Thubert (pthubert) wrote:
> [Pascal] I'm modifying / adding the following text in the draft to amend 6437:
> 
>   In a LLN, each transmitted bit represents energy and every saving
>   counts dearly.  Considering that the value for which the Flow Label
>   is used in the IPv6 Flow Label Specification [RFC6437] is to serve
>   load balancing in the core, it is unlikely that LLN devices will
>   consume energy to generate and then transmit a Flow Label to serve
>   interests in some other place.  On the other hand, it makes sense to
>   recommend the computation of a stateless Flow Label at the root of
>   the LLN towards the Internet.
> 
>   Reciprocally , [RFC6437] requires that once set, a non-zero flow
>   label value is left unchanged.  The value for that setting is
>   consumed once the packet has traversed the core and reaches the LLN.
>   Then again, there is little value but a high cost for the LLN in
>   spending 20 bits to transport a Flow Label from the Internet over the
>   constrained network to the destination node.  It results that the
>   MUST in [RFC6437] should be alleviated for packets coming from the
>   outside on the LLN, and that it should be acceptable that the
>   compression over the LLN erases the original flow label.  It should
>   also be acceptable that the Flow Label field is reused in the LLN as
>   proposed in this draft.
> 
> What do you think?

Disagree. No matter how many words are put around it, it's still violating RFC6537. This is not a question of hypothetical value or cost. I'm still waiting for your energy analysis on those 20 bits. "Low energy" can be used as a hand-wavy argument to do a lot of things which are bad in retrospect. 

Phil