Re: [6lowpan] ND-18 Multiple Prefix

Carsten Bormann <cabo@tzi.org> Fri, 03 February 2012 17:44 UTC

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From: Carsten Bormann <cabo@tzi.org>
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Date: Fri, 3 Feb 2012 18:43:53 +0100
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To: Tom <my.mailing.acc@gmail.com>
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Subject: Re: [6lowpan] ND-18 Multiple Prefix
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On Feb 3, 2012, at 18:32, Tom wrote:

> Hello Everyone,
> 
> Kindly clarify does ND-18 support multiple prefix (and multiple address/node derived from these prefixes). 
> I raise this doubt because the assumption section,  bullet 4 says -> a 6lowpan is configured with one or more prefixes,
> and the final bullet says -> since the 6lowpan shares one single prefix through out the network.

Yes, this editorial problem was noted by Adrian Farrel in the IESG review as well.

Fix:
s/shares one single prefix/shares its prefix(es)/

(The point of the sentence was that prefixes are lowpan-wide and thus you don't have a separate prefix for each link, not that there is only one prefix.  Bad wording.)

The expectation is that the number of these prefixes is going to be low.
Due to renumbering, we can't really rule out a situation where there is more than one prefix.

> Further, if 6LBR is advertising multiple prefix and host configures multiple global addresses based on these prefix how will they be useful.

Mostly in a renumbering situation, I think.

> Will not the 6LR/6LBR reject registration through ARO from different source address but same EUI-64 (same node auto configuring with different prefixes).

No, it would reject multiple nodes registering the same address, but there is no problem with one node registering multiple addresses.  Beside multiple prefixes, you may want to have one address based on a EUI-64 and another one based on a 16-bit MAC address (see RFC 4944) or you might even want an additional temporary address as a privacy address.  The EUI-64 is there in the ARO so the 6LBR can find out wether multiple nodes are trying to register the same address -- this is most likely to happen for 16-bit-based addresses, of course.

Grüße, Carsten