dhcpinform or dhcprequest

Tom Schmitt TomSchmitt at gmx.de
Wed Sep 2 12:16:34 UTC 2009


I have a question about the DHCP protocoll, I'm not sure if I understand it correctly.

Normally (I thought) a client would at first send a DHCPDISCOVER, gets an offer, sends a request and finally gets an acknowledge from the DHCP server. 
And, at least with my configuration, the DHCP server is sending an update to the DNS with the name and IP of the client.

So far no problem.

But the first lease the client is getting from the DHCP server has only a short leasetime and the client is requiered to renew the lease.

Now to the question:
In my understanding the client should at some point before the leasetime is ended (normally at half the leasetime) send a DHCPREQUEST to renew its lease. Then the DHCP server would send a DHCPACK with a longer leastime.

But what I see in the logfile of the DHCP server is something else:
At half of the leasetime the client is sending a DHCPINFORM instead of a DHCPREQUEST.
The DHCP server is answering with a DHCPACK but the leasetime stay the same, the lease is not renewed. A few minutes later the leasetime is ended and the DHCP server sends an update to the DNS, deleting the entry of the client.
But the client still uses this IP, only now having trouble because of the missing DNS entry.

My question:
Is this really a problem on clientside? (If yes, know anyone a solution for this?)

Or is this a bug on side of the DHCP server (version 3.1.2) ?
Maybe with a well known solution ;-)

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