http://isc-dhcp-users.193.s1.nabble.com/randomly-assign-ip-s-from-dynamic-address-range-tp156p189.html
> Most dhcp clients also store the last address. So even if you configure
> the server to offer different IPs to the client, the client could keep
> asking for the old address and the server would accept that.
>
> regards,
> -glenn
>
> On Tue, June 9, 2015 12:58 am, Bob Harold wrote:
>> A Windows 8 client appears to keep the last IP in the registry in:
>> HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\{...<Network
>> Adapter>...}\DhcpIPAddress
>>
>> Although many years ago I remember having clients that remembered the
>> last
>> 5 or 10 IP's (in different subnets).
>>
>>
>>
>> --
>> Bob Harold
>> hostmaster, UMnet, ITcom
>> Information and Technology Services (ITS)
>>
[hidden email]
>> 734-647-6524 desk
>>
>> On Mon, Jun 8, 2015 at 9:11 AM, Glenn Satchell
>> <
[hidden email]>
>> wrote:
>>
>>>
>>> On Mon, June 8, 2015 7:29 pm, Arne Baeumler wrote:
>>> > Hi Simon,
>>> >
>>> > thank you for your reply.
>>> >
>>> > On 2015-06-05 15:05, Simon Hobson wrote:
>>> >> Hmm, that's a variation I don't think we've seen before ;-)
>>> >> What you are seeing is correct operation according to the RFCs - the
>>> >> server is required to keep the address stable as far as is possible,
>>> and
>>> >> that means the client can come back after an arbitrary length of time
>>> >> and as long as the address has not been re-used then the client
>>> *must*
>>> >> get the same address.
>>> >
>>> > Would you please point me to the RFC you are referring to?
>>> > Can't find any requirements for the server to maintain some kind of IP
>>> > history in RFC2131.
>>> >
>>>
>>> I'm looking at
https://www.ietf.org/rfc/rfc2131.txt, there are
>>> several
>>> references to this feature within the document. Section 4.3.1 is the
>>> clearest on this, even though it says it "SHOULD" rather than "MUST"
>>> be
>>> done this way.
>>>
>>> 1.6 Design goals
>>>
>>> o Retain DHCP client configuration across DHCP client reboot.
>>> A
>>> DHCP client should, whenever possible, be assigned the same
>>> configuration parameters (e.g., network address) in response
>>> to each request,
>>>
>>> o Retain DHCP client configuration across server reboots, and,
>>> whenever possible, a DHCP client should be assigned the same
>>> configuration parameters despite restarts of the DHCP
>>> mechanism,
>>>
>>> 2.2 Dynamic allocation of network addresses
>>>
>>> The
>>> allocation mechanism (the collection of DHCP servers) guarantees
>>> not
>>> to reallocate that address within the requested time and attempts
>>> to
>>> return the same network address each time the client requests an
>>> address.
>>>
>>> 4.3.1 DHCPDISCOVER message
>>>
>>> When a server receives a DHCPDISCOVER message from a client, the
>>> server chooses a network address for the requesting client. If no
>>> address is available, the server may choose to report the problem
>>> to
>>> the system administrator. If an address is available, the new
>>> address
>>> SHOULD be chosen as follows:
>>>
>>> o The client's current address as recorded in the client's
>>> current
>>> binding, ELSE
>>>
>>> o The client's previous address as recorded in the client's
>>> (now
>>> expired or released) binding, if that address is in the
>>> server's
>>> pool of available addresses and not already allocated, ELSE
>>>
>>> o The address requested in the 'Requested IP Address' option,
>>> if
>>> that
>>> address is valid and not already allocated, ELSE
>>>
>>> o A new address allocated from the server's pool of available
>>> addresses; the address is selected based on the subnet from
>>> which
>>> the message was received (if 'giaddr' is 0) or on the address
>>> of
>>> the relay agent that forwarded the message ('giaddr' when not
>>> 0).
>>>
>>> I hope this helps.
>>>
>>> I realise this doesn't help with your original question :) In terms
>>> of
>>> privacy there is an IPV6 feature that assigns a new IP address each
>>> day.
>>> This is part of the client functionality defined in RFC 4941 "Privacy
>>> Extensions for Stateless Address Autoconfiguration in IPv6" but
>>> doesn't
>>> help with your current IPv4 issue.
>>>
>>> regards,
>>> -glenn
>>>
>>>
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>>>
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