How to make dhclient forget its last DHCP lease?

Solution 1:

This did the trick for me(for eth0, run from sudo su):

dhclient -r -v eth0 && rm /var/lib/dhcp/dhclient.* ; dhclient -v eth0

Solution 2:

DHCP Client program writes the lease to a file. Just delete the file and restart networkmanager.

/var/lib/dhcp/dhclient.leases

This is where the leases are stored, in my computer.

Solution 3:

What you are seeing is not your machine remembering the IP. In syslog you see DISCOVER REQUEST OFFER ACK however this is not in the order that it happened. It actually went DISCOVER OFFER REQUEST ACK to confirm this you can sniff the traffic between the PC and upstream DHCP server. You sent DISCOVER the server sent back OFFER and you got the IP from the OFFER for your REQUEST

You did everything right however, when you did "dhclient -r" dhclient will send a unicast RELEASE and some ISPs only accept multicast packets to their DHCP server, so the RELEASE never got there, as far as the server is concerned your lease is still valid, so it gave you back the same IP in the OFFER.