Two different IP addresses leased out to the same device
Simon Hobson
dhcp1 at thehobsons.co.uk
Wed Sep 9 15:45:12 UTC 2009
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.
--
Simon Hobson
Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
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