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And if so, how is this supposed to work? Is the client supposed to attach the interface identifier himself, based on the interface the assignment came through?

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While I can't think of any valid reason to do so, it's not mentioned/forbidden anywhere. Is this just curiosity, or why would you want to do this? – Hugo May 19 '14 at 11:25

Interesting. The RFCs don't mention anything about using link-local. I just tried it with a Juniper SSG5 as DHCPv6 server and Mac OS X Lion as client, and it did seem to work :-) The interface that received the DHCP packet became the outgoing interface for the request.

It can make debugging awfully complicated though...

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are you sure? i'm using mac os x lion, too, and when my radvd distributes a link-local dns via RDNSS, i dont get an interface identifier on the IP set by mac os and all DNS requests time out. Also, leaving RDNSS/DHCPv6 apart - the network dialog does not even allow the IP address to contain a % character, if you want to configure the DNS manually – barbaz Sep 3 '11 at 13:02
I just checked with Wireshark, and you are right, I don't see the request. Must have been either cached settings or cached results. – Sander Steffann Sep 3 '11 at 21:48
So: new conclusion! Although it could work it's not implemented at the moment, so don't use link-local addresses for DNS! :-) – Sander Steffann Sep 3 '11 at 21:49

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