Re: [Roll] [6tisch] Support of flow label to carry the RPL information in data packets

Brian E Carpenter <brian.e.carpenter@gmail.com> Thu, 17 April 2014 20:31 UTC

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Date: Fri, 18 Apr 2014 08:31:30 +1200
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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To: Fernando Gont <fernando@gont.com.ar>
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Cc: "6man@ietf.org" <6man@ietf.org>, roll <roll@ietf.org>, "6tisch@ietf.org" <6tisch@ietf.org>, Ines Robles <mariainesrobles@googlemail.com>
Subject: Re: [Roll] [6tisch] Support of flow label to carry the RPL information in data packets
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Fernando,

On 18/04/2014 02:49, Fernando Gont wrote:
> Hi, Pascal,
> 
> On 04/17/2014 11:27 AM, Pascal Thubert (pthubert) wrote:
>> Considering the support we have at 6TiSCH and ROLL for the work, I
>> published draft-thubert-6man-flow-label-for-rpl-00.txt to the 6MAN WG.
>>
>> The main discussion is probably to confirm whether our proposed use of
>> the flow label inside the RPL domain is compatible with the goals that
>> are achieved by RFC6437. Let us continue the discussion there from now on.
> 
> I just skimmed through the I-D. Two quick questions:
> 
> 1) Does your document propose/require that the Flow Label be rewritten
> by some border router? -- I ask because, at the time, there was strong
> opposition to this.

It was of course contested, but we have to remember that the flow label
is an unauthenticated field, so our interpretation of it has to be
robust against altered values. RFC 6437 indeed covers the case where a
forwarding node sets the flow label.

> 2) Does the algorithm/scheme with which you'll rewrite the Flow-Label
> lead to predictable sequences? And/or, would the resulting values have a
> uniform distribution?

The same part of RFC 6437 does RECOMMEND a uniform distribution.

Also, the very first paragraph of RFC 6437 states that "a flow is not
necessarily 1:1 mapped to a transport connection", so there is reasonable
flexibility.

    Brian

> 
> Thanks!
> 
> Best regards,