DHCPd problem with PXE/Windows clients - multiple leases

Simon Hobson dhcp1 at thehobsons.co.uk
Tue May 8 15:52:53 UTC 2007

David Rickard wrote:

>We've got three DHCP servers on three sites, running the ISC DHCP daemon
>on SuSE Linux Enterprise Server 10. We also have Zen for Desktops 7 (SP1
>Hotfix 3) on all three sites running on Netware 6.5.
>My problem is that when the PC boots, it ends up with two leases - one
>for when the PXE runs, and another for when Windows boots!

We knew that was going to be the problem before even opening the mail !

If you looked in the archives, going back as far as a week or two, 
you'd find more than one discussion of this common problem. It's 
caused by Windows using the hardware MAC address as the client 
identifier, while PXE (and Linux, and a few others) don't. The 
client-id is the primary database key, with MAC address used if 
client-id isn't supplied - hence as far as the server is concerned 
these are two different clients.

Solutions include :

1) Don't run Windows, it's a pain in the network ;-)

2) Persuade Windows to do something different - good luck !

3) Configure all clients to use the same client id

4) set up a pool just for PXE clients and give it a short lease time 
(to allow reuse)

5) make sure the pool is big enough for all clients to have two addresses

6) Apply Didis patch that fiddles with the client-id

7) Wait for a future version of the server that allows the admin to 
specify the key to be used.

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