dhcpinform or dhcprequest

[Shawn Holland]

On Wed, 2009-09-02 at 17:22 +0200, Tom Schmitt wrote:
> -------- 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 
> > >of a DHCPREQUEST.
> > >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.
> 

To me it sounds like a broken client as its up to the client to renew
its lease. The DHCP server can only tell it when the lease expires but
not when to renew.

As for troubleshooting the client, for what its worth, you could try
resetting the IP stack from a command line with:

netsh int ip reset reset.txt

This helps a lot of weird IP issues.

-- 
Regards,
Shawn Holland
Sandara Technologies Ltd.