force to only accept hardware address as dhcp-client-identifier

Nomad atxnomad at
Tue Jan 29 17:41:40 UTC 2008

On 1/29/08, Tarik Gasmi <isnogoud at> wrote:
> Hello,
> the isc dhcp server identifies dhcp clients by the
> dhcp-client-identifier they send. this can be different
> for each client depending on the dhcp-client config:
> - host-name
> - vendor-code
> - some string
> - ...
> - hw-address
> if no dhcp-client-identifier is sent by the client, the server uses the
> hardware address as identifier.
> we have the problem, that we are serving thousands of clients, and
> different clients with coincidently the same hostname could be
> configurated to send their hostname as identifier. So we get the
> duplicate-hostname-problem and we cannot force all users to configurate
> their dhcp-clients in a certain (some users don't even know which
> dhcp-client they are using)
> is there a way to force/configure the dhcp-server, so that it only
> chooses hardware address of the client as valid identifier no matter
> what other dhcp-client-identifier the client is sending?
> thanks and best regards
> tarik gasmi

With multi-boot machines this has become more of an issue.  Each time the
computer boots into a different environment, a new identifier may be used
and so the machine may be associated with multiple IP addresses.  If you're
attempting to manage these devices, instead of one IP address per NIC, you
now have two, three maybe four IP address entries for one physical device.
 In addition, if you have long lease times it could mean more work for the
server as it attempts to figure out which leases are actually in use (I'm
probably wrong on this)

We have an in-house patch that will use the hardware address as the
identifier but I'm not sure if we can make it available to others.  I've
asked and will respond off-list to anyone interested.
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