Automatic remove lease from pool

[Henrik Sterndorff Jessen]

Hi

I am using dhcp to dish out fixed addresses to users. All users are
connected to cisco switch ports that act as a relay and therefore add
option-82 information to the dhcp query. I don't know the mac addresses
of the users.

I am assigning a fixed address to each user using a configuration like:

----
class "myClass" { match if (substring ((option agent.circuit-id),4,2) =
09:02); }

subnet 10.0.0.0 netmask 255.255.255.0 {
	option routers			10.0.0.1;
	pool { allow members of "myClass"; range 10.0.0.5 10.0.0.5; }
}
----

But this writes a lease binding users actual mac address to the ip
address 10.0.0.5. So if the user changes hardware I get a "no free
leases" error in the logfiles and nothing works until the lease expires.

Setting the lease time very low is not an option since I have a ton of
users on the dhcp server and it kills the cpu and network. Yes... I have
tried :)

Other option is creating a script that watches the logfile and
automatically edits the lease files when the log error occurs. But that
requires a dhcpd restart, which is not sexy.

Any way to force the dhcp server to automatically overwrite leases in
this kind of setup?

Thanks for any help...

Regards,
/Henrik