How to identify a client?

Tom Schmitt TomSchmitt at
Mon Jul 7 07:02:15 UTC 2008


thank you for your answer. Your first solution doesn't work for me, because I have several different subnets. So I can't give the client the same IP-Address in different subnets.
As a second point I don't know all the MAC-addresses before the clients is connected to the network.

Your second solution I don't understand completly: Is the DHCP-identifier from the clilent the same, even if the MAC-address is changed?


-------- Original-Nachricht --------
> Datum: Fri, 04 Jul 2008 18:27:27 +0200
> Von: Sten Carlsen <sten at>
> An: dhcp-users at
> Betreff: Re: How to identify a client?

> I have a similar situation, but with a few differences. I hope this 
> could be an inspiration.
> I have made a host entry for each of the MACs (wired / wireless)they are 
> each given the same IP, that works without any problem. I can even 
> continue a download while switching form wired to wireless.
> The other thing I have tried is to have a host entry with a  option 
> dhcp-client-identifier. IIRC this also works.
> Tom Schmitt wrote:
> > And now comes the problem: In the WLAN the client is using another MAC
> > (the one of the WLAN-card instead of the normal NIC) but the same name. So,
> > if a client was first in a normal subnet, getting a lease and a DNS-entry,
> > then the client is moving to a WLAN-subnet and comes with the same name but
> > differrent MAC to the DHCP. The clienst is getting a new IP but no entry
> > in the DNS because there is already an entry and the TXT-records says: Its
> > not yours!
> >
> > So, for the time the old lease is valid, the client has no DNS-entry.
> >
> > What can I do to solve the problem?
> > The only thing I could think of, was a shorter leasetime. But this is
> > problematik for several other reasons. Abd beside: It wouldn't solve the
> > problem, only make it happen fewer times than with a longer lease.
> >
> > Is there a best practice to avoid this problem? Do anyone else have the
> > same problem?
> >

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