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

"Pascal Thubert (pthubert)" <pthubert@cisco.com> Thu, 17 April 2014 17:08 UTC

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From: "Pascal Thubert (pthubert)" <pthubert@cisco.com>
To: Fernando Gont <fernando@gont.com.ar>, "6man@ietf.org" <6man@ietf.org>
Thread-Topic: [6tisch] [Roll] Support of flow label to carry the RPL information in data packets
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Date: Thu, 17 Apr 2014 17:08:02 +0000
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Cc: "6tisch@ietf.org" <6tisch@ietf.org>, Ines Robles <mariainesrobles@googlemail.com>, roll <roll@ietf.org>
Subject: Re: [Roll] [6tisch] Support of flow label to carry the RPL information in data packets
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Hello Fernando

Thanks for your review, and we can certainly use some piece of advice from you here:

1) Yes, the idea is that leaves of a RPL network do not use the flow label. Inside the RPL domain it is used to support RPL operations. 
At the border router, which is a RPL root, it is finally set to the value that is visible in the Internet. I can expect some knee jerk about this proposal but before rejecting in on some principle we must consider the benefits in IoT applications, and whether the interests that the flow label serves in the core can still be enabled with this proposal.

2) The draft did not finalize the way the Flow Label is computed in the Internet side. If we agree on the principle then we can work out the details.

To give you an idea, my mind is to compute classically a hash for a given flow.

The root is expected to have a policy that indicates whether the original source address is relevant or not in the identification of a flow (it is not for a compound flow that we do not want to see separated in the Internet). The instance ID that is in the original flow label is certainly relevant and is used in the hash computation. A random computed by the root at boot would be useful as well.

We expect few flows to emerge from a given RPL root, and even fewer from a given constrained device.
The random and the hash are really there to enable load balancing between flows out of different backbone routers.


Cheers,

Pascal


> -----Original Message-----
> From: Fernando Gont [mailto:fernando@gont.com.ar]
> Sent: jeudi 17 avril 2014 16:49
> To: Pascal Thubert (pthubert); 6man@ietf.org
> Cc: 6tisch@ietf.org; Ines Robles; roll
> Subject: Re: [6tisch] [Roll] Support of flow label to carry the RPL information
> in data packets
> 
> 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.
> 
> 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?
> 
> Thanks!
> 
> Best regards,
> --
> Fernando Gont
> e-mail: fernando@gont.com.ar || fgont@si6networks.com PGP Fingerprint:
> 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1
> 
>