The DHCP server is indeed very sticky, and intentionally so. If the
pool of available IP addresses is not exhausted, then a given machine
will continue to receive the same IP address, even if the lease has
expired. If the pool does fill up, then the server will reuse IPs,
starting with the one whose lease expired the longest ago.
It doesn't help to unregister and re-register the computer - the old
lease will still be remembered once the computer is re-registered.
On Thu, Feb 26, 2009 at 08:41:39PM -0500, Kramer, Jack wrote:
> You could also use something like nmap to give you the likely vendor of the
> rogue machine, so you had a good basis to work off of when it came to
> tracking them down, and then follow up with a more, um, personal method of
> troubleshooting. Remember, gloved hands help keep from leaving marks.
> Seriously though, the DHCP server is pretty sticky - I believe that once
> you've registered a machine it will keep assigning that IP to the same
> machine for quite a while. I don't know if unregistering the machine from
> dhcp.msu.edu and re-registering it will help. AFAIK, the period of "quite a
> while" is on the order of months.
> Jack Kramer
> Computer Systems Specialist
> University Relations, Michigan State University
> From: Al Puzzuoli <[log in to unmask]>
> Reply-To: Al Puzzuoli <[log in to unmask]>
> Date: Thu, 26 Feb 2009 19:19:51 -0500
> To: <[log in to unmask]>
> Subject: Re: [MSUNAG] How to force a new IP address from DHCP?
> How about this:
> Bring up the machine in question, let it register and obtain the bad IP.
> Shut down the machine without unregistering it.
> Plug in a cheap Linksys router, or some similar box, connect the PC to
> the router and rerun the DHCP registration. This should register the
> MAC of the router and give it a different IP. Of course now, the PC
> will be behind a NAT firewall, but I wouldn't think that should present
> a problem in most scenarios.
> Al Puzzuoli
> Michigan State University
> Information Technologist
> Resource Center for Persons with Disabilities
> 120 Bessey Hall East Lansing, MI 48824-1033
Doug Nelson, Network Architect | [log in to unmask]
Academic Technology Services | Ph: (517) 353-2980
Michigan State University | http://www.msu.edu/~nelson/