dhcpinform or dhcprequest

Tom Schmitt TomSchmitt at gmx.de
Wed Sep 2 15:22:54 UTC 2009

-------- Original-Nachricht --------
> Datum: Wed, 2 Sep 2009 13:39:44 +0100
> Von: Simon Hobson <dhcp1 at thehobsons.co.uk>
> An: Users of ISC DHCP <dhcp-users at lists.isc.org>
> Betreff: Re: dhcpinform or dhcprequest

> >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.
> Correct
> >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 
> >The DHCP server is answering with a DHCPACK but the leasetime stay 
> >the same, the lease is not renewed.
> DHCP Inform is not for lease renewal - it is separate and is designed 
> to allow applications to query the server for options. Internet 
> Explorer is a well known example of this, it will do a DHCP Inform to 
> find out if it should be using a proxy (amongst other stuff).
> >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?)
> Yes, it's a broken client - very broken.
> Hard to see how much more broken it could be.
>   - Attempts to renew using DHCP Inform
>   - Fails to renew
>   - Continues using address
> Solution, ditch the client ! Of course, if the vendor can fix it then 
> demand that they do.

Thank you for the good explanation. This is very helpfull.

Sadly I have not much hope that the vendor will change anything: The Client is a HP workstation with Windows XP and Microsoft is not well known for changing their software based on a request from a single person.

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