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Re: [6lo] Future extensibility for the DAR/DAC

Charlie Perkins <charles.perkins@earthlink.net> Tue, 22 May 2018 14:50 UTC

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To: "Pascal Thubert (pthubert)" <pthubert@cisco.com>
Cc: "6lo@ietf.org" <6lo@ietf.org>
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From: Charlie Perkins <charles.perkins@earthlink.net>
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Date: Tue, 22 May 2018 07:49:54 -0700
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Subject: Re: [6lo] Future extensibility for the DAR/DAC
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Hello Pascal,

Seems we are mostly in agreement.  But see below...

On 5/21/2018 10:38 PM, Pascal Thubert (pthubert) wrote:

>
>> Another possibility would be to reserve some initial bits of the ROVR 
>> field itself to indicate the length of the ROVR.   Old-legacy nodes 
>> would still discard new DAR and DAC messages with a ROVR that was too 
>> long. New-legacy nodes would know to check the first three or four 
>> bits of the field for the length of the ROVR.  But I did not think 
>> this all the way through yet.
>>
>
> But old legacy will set those bits randomly. And then we have 
> alignment problems. I proposed the subcode as a last resort...

I don't think it's a problem for old legacy.  New-legacy 6LR should 
detect old-legacy 6LN and maintain legacy-ness as part of the 
registration state.  ROVR would have sizes of 61, 125, 189, or 253 
bits.  Again, not a problem, and alignment is not an issue.

Plus as a bonus we get to have our Code back as a normal Code field.

It just needs to be checked that new-legacy 6LR can detect old-legacy 6LN.

Regards,
Charlie P.

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