DHCPv6 and MAC Address inclusion

perl-list perl-list at network1.net
Wed Jan 25 20:35:21 UTC 2012

It SEEMS like the windows machine is using the MAC although I am not sure of DUID vs IAID and where each can be seen. 

I just disabled / enabled adapter on test windows7 laptop here ... I have some numbers available (sans packet capture) from logs and from the leases file (dhcpd ): 

00:15:c5:14:ce:b0 (the actual mac of the windows computer) 
dhcpd: Client 00:01:00:01:13:e0:fd:f1: 00:15:c5:14:ce:b0 releases address 2620:0:2e50:e8:1::f541 (line from the log file - I assume that is DUID - seems to contain full mac) 
ia-na "\305\025\000\020\000\001\000\001\023\340\375\361\000\025\305\024\316\260" (Opener to the lease entry in leases file - i have no idea what that string of stuff is) 

----- Original Message -----

> From: "Michael Dean Pugh" <mdpugh at hotmail.com>
> To: dhcp-users at isc.org
> Sent: Wednesday, January 25, 2012 3:00:05 PM
> Subject: Re: DHCPv6 and MAC Address inclusion

> I'm jumping in at the end here and not responding to any particular
> post. I
> have followed this thread with great interest. This seems like a good
> time to
> make an observation and ask a question.

> There is much talk about deriving the MAC address from IPv6
> identifiers.
> While it's true that in most cases (every case I've personally
> observed--
> Windows and FreeBSD) the MAC is part of the DUID, this is only useful
> if the
> host has one interface as the DUID is unique to the host not the
> interface (I
> think we're all in agreement here). Also, once the host has assigned
> itself
> the DUID, the interface can be replaced, but the DUID will remain the
> same, so
> the MAC address derived from the DUID at this point would be invalid.
> Again,
> this is with Windows and FreeBSD.

> Now, the observation. Microsoft encodes the first 24 bits of the MAC
> address
> (the manufacturer portion) in the IAID by directly copying them into
> the last
> 24 bits of the IAID. In other words, if the MAC is 01:23:45:ab:cd:ef,
> the
> IAID is xy012345(Hex) for some x and y. This has limited usefulness
> since it
> is entirely possible to have more than one interface from the same
> manufacturer installed in one host (it seems like it would have made
> more
> sense to have used the last 24 bits of the MAC).

> This brings me to the question. Does anyone know how the first 8 bits
> of the
> IAID are derived by Microsoft? I'm pretty sure I found this somewhere
> on the
> Internet, but have been unable to find it again. I'm also wondering
> if
> Microsoft's IAID algorithm is based on any standards or if the IAID
> is merely
> a 32-bit number. It does seem that the IAID holds enough information
> to
> uniquely identify each interface on a single managed network.

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