Two different IP addresses leased out to the same device

[Sten Carlsen]

Hi

In this case I see that the requests com in from different circuit-id
and remote-id.

I would have thought that would mean different network segments. Unless
of course that this is caused by trying to hide the real information?


Simon Hobson wrote:
> Markus Zuercher wrote:
>
>> I have one device which constantly receives different IP addresses
>> given out from a single DHCPD 4.1.0 server.
>>
>> For a better understanding, this is the lease database of the server:
>>
>> lease 10.10.0.2 {
>>   starts 3 2009/09/09 14:24:53;
>>   ends 4 2009/09/10 14:24:53;
>>   tstp 4 2009/09/10 14:24:53;
>>   cltt 3 2009/09/09 14:24:53;
>>   binding state active;
>>   next binding state free;
>>   hardware ethernet xx:xx:xx:xx:xx:xx;
>>   uid "\001\000\011k\007\346z";
>>   option agent.circuit-id 0:96:0:41;
>>   option agent.remote-id 0:1e:69:xx:xx:xx;
>>   client-hostname "privat";
>> }
>> lease 10.10.0.238 {
>>   starts 3 2009/09/09 14:28:14;
>>   ends 4 2009/09/10 14:28:14;
>>   tstp 4 2009/09/10 14:28:14;
>>   cltt 3 2009/09/09 14:28:14;
>>   binding state active;
>>   next binding state free;
>>   hardware ethernet xx:xx:xx:xx:xx:xx;
>>   option agent.circuit-id 0:8a:0:41;
>>   option agent.remote-id 0:18:9b:xx:xx:xx;
>>   client-hostname "support-laptop";
>> }
>
> Frank has hinted at this, I'll expand and explain.
>
> As far as the server is concerned, they are different clients as
> required by the RFC.
>
> One lease has a UID (aka Client-ID) which therefore forms the primary
> key in the database - the other has no UID and so the server falls
> back to using the MAC address.
>
> This is a longstanding issue when a machine boots with multiple DHCP
> clients - and it's mostly down to Microsoft that the problem exists.
> The RFC doesn't specify what should be in the Client-ID, and Microsoft
> decided that putting the MAC address in there made sense. This isn't
> wrong, just different to everyone else who default to not supplying a
> Client-ID at all.
>
> It first started popping up when people were multi-booting into
> Windows and other OS's like Linux. Then PXE came along and added to
> it. There have been patches to fudge the request packets (either
> remove the Client-ID or add it).
>
> A proposed feature that I believe never made it was to allow the
> administrator to configure the database key - it currently defaults to
> "pick-first(client-id, hardware)". If changed to just plain "hardware"
> then Client-ID would be ignored.
>