Re: New Version Notification for draft-chakrabarti-nordmark-6man-efficient-nd-05.txt

Erik Nordmark <> Mon, 03 March 2014 15:02 UTC

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Date: Mon, 03 Mar 2014 15:01:55 +0000
From: Erik Nordmark <>
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To: 神明達哉 <>
Subject: Re: New Version Notification for draft-chakrabarti-nordmark-6man-efficient-nd-05.txt
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On 3/2/14 4:40 PM, 神明達哉 wrote:
> At Sat, 01 Mar 2014 14:01:03 +0100,
> Erik Nordmark <> wrote:
>> To have a unicast RA prior to having registered the link-local address,
>> the router needs to use the SLLA option in the RS - this would be the
>> same mechanism as in the draft for sending errors to NS/AROs.
> What if the link-local address is a duplicate and that's because the
> link-layer address is a duplicate?  If the unicast RA is supposed to
> include an ARO whose status field is 1 and be sent to the (duplicate)
> link-local address, it's not guaranteed the RA is delivered to the
> node that sent the RS.
We can not detect and handle duplicate MAC addresses using DAD in general.

Even back when we first defined DAD we knew it could handle MAC address 
duplicates for Ethernet (assuming certain device driver behavior), but 
probably not on FDDI and Token Ring (due to how the ring maintenance 

More recent work like dad-proxy assumes that the MAC addresses  are not 
duplicate, and the loopback case needs special care even when MAC 
addresses are unique.

Using explicit registrations doesn't really change that. The 
registration needs some unique id (be it an EUI-64 or DCHP DUID) that is 
unique to tell apart a duplicate and a registration refresh. If your MAC 
address is not unique then your EUI-64 (or MAC address based DUID) is 
likely to also not be unique.