How to identify a client?

Tom Schmitt TomSchmitt at gmx.de
Fri Jul 4 15:23:53 UTC 2008


Hi,

I'm running ISC-dhcpd which is running fine. I use dynamic DNS-Update which is also working fine and the TXT-record the dhcpd adds in the DNS makes sure, nobody else will occupy this name while the lease is lasting. The leasetime is one day in all subnets.

So far, so good.

Now I have besides all my normal subnets a few WLAN-subnets, also using DHCP. And of course there are Clients switching from a normal subnet to a WLAN-subnet and back. 
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?

Bye,
Tom.

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