host-identifier with IPv6

[Frank Sweetser]

Ted Lemon wrote:
> On Mar 1, 2009, at 7:05 PM, Frank Sweetser wrote:
>> That says to me that if a server attempts to extract the HW address 
>> that was
>> used to generate a given DUID, it's violating the RFC.
> 
> Only if it's using it for protocol purposes.   You can do anything you 
> want with it as long as it doesn't affect your processing of the 
> protocol.   The point of this text is to prevent you from doing 
> something naive with the identifier, like simply treating the Mac 
> address portion as an identifier and ignoring the rest of it.

The problem is, that's exactly what I and others would like to do.

DHCPv4 comes very close to allowing people to do that, and yet every other 
month or so someone still emails the list asking if there's a way to pretend 
that the client identifier really is the HW address, because they've built all 
of their configuration assignments around the HW address.

Let me propose a scenario.  Assume that you have a client with a HW address of 
XX, and two different operating systems installed.  OS A has generated (and 
properly stored) a DUID of AAXX, and OS B has generated BBXX.  The DHCP server 
has a configuration block for the host:

host foo {
   fixed-address6 2001::1
   host-identifier hwaddress XX
}

Host A comes along, and obtains a lease for address 2001::1.  Now, while the 
lease is still valid, the machine is unplugged from the network, powered down, 
plugged back into the network, and booted into OS B.  OS B will then try to 
obtain an address via DHCPv6.

In DHCPv4, both operating systems would obtain the same IP address.  Would 
this same behavior be legal in DHCPv6?

And what if, rather than a fixed address, the address assignment were a 
dynamic one?  In DHCPv4, the client would get a different address, but a 
number of people would be happy if it were legal for it to get the same one 
instead.

-- 
Frank Sweetser fs at wpi.edu  |  For every problem, there is a solution that
WPI Senior Network Engineer   |  is simple, elegant, and wrong. - HL Mencken
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