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

Carsten Bormann <cabo@tzi.org> Fri, 26 October 2012 12:56 UTC

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From: Carsten Bormann <cabo@tzi.org>
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Date: Fri, 26 Oct 2012 14:56:22 +0200
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To: "Pascal Thubert (pthubert)" <pthubert@cisco.com>
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Subject: Re: [Roll] using the flow label instead of hop by hop
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On Oct 26, 2012, at 14:19, "Pascal Thubert (pthubert)" <pthubert@cisco.com> wrote:

> In any fashion, the flow label cannot be used to transport valuable information because it cannot be verified on the receiving side. 

I hear that a lot.
Most of our current protocols are indeed designed to ignore v6 specific IP header fields.
But just to give a very accessible example: A v6 specific version of ESP (RFC4303) could use the label to transmit the SPI.

I'm not saying this because I want to rule out the use of the label for forwarding fabric purposes; it's just that with more focus on IPv6, hosts may find good uses for the label.  But using the label from RPL-cognizant nodes, e.g for router-sourced packets or for the outer header of the RPL tunnel, should be fine (if there is a way to detect that this has happened).  Overwriting the label when a previously formulated IPv6 packet enters the RPL instance is bad for the same reasons adding the RFC 6553 RPL hop-by-hop option or the RFC 6554 routing header in the middle of the path would be bad.

Grüße, Carsten

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