IPCONFIG /release & /renew question

I have a machine at work that is getting a conflicting IP address message. The machine is setup for DHCP. I have done an IPCONFIG /RELEASE and /RENEW on it but DHCP likes to keep handing back the same IP address it previously had.

My guess is someone set a machine somewhere with a static IP and DHCP thinks that is a free address and keeps handing it out. While finding the machine with the incorrect static address is being looked in to I was wondering if there is a way to ask for a new IP address from the DHCP server and force the DHCP server to choose an entirely different address rather than the one it keeps handing out.

Any way to do that?

(FYI: Fiddling with the scope on the DHCP server is not an option as we do not have control/access to it)

Well, if you ask with a different MAC address, you’ll get a different IP address from DHCP. You could swap out the network card in your box, or (if your card/driver permit) manually specify a different MAC address than the one that’s hard-coded.

If you unplug this PC and plug in a “sacrificial” PC, it will hopefully be handed the “bad” IP so you can plug in your PC again, release and renew, and get a good IP. That’s assuming the DHCP server doesn’t just assign the same IP to the MAC address.

Failing that, can you do a netsend to the offending PC that’s apparently got a static IP and wait for its user to contact you?

No. The DHCP server has a lease period. The sacrificial PC would be given a new address; the original PC wuld still have the bad address reserved. For this plan to work, you’d have to leave both PCs unplugged until the DHCP lease period had lapsed.

In other words, your “…assuming the DHCP server doesn’t just assign the same IP to the MAC address” is exactly what a DHCP server does… consistently assigns the same IP address to the same MAC address as long as the lease is active.