How to make dhclient forget its last DHCP lease?

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http://askubuntu.com – What I'm trying to achieve is to get cold-start, zero-state DHCP lease which means forcing dhclient through the full discovery and configuration process (DHCPDISCOVER–DHCPOFFER–DHCPREQUEST–DHCPACK as opposed to the shortcutted DHCPREQUEST–DHCPACK cycle which uses a remembered address). I need this to debug a network configuration problem. I have tried: flushing current lease with dhclient -r, disconnecting the current Network Manager connection; killing any leftover dhclient and dnsmasq processes; cleaning /var/lib/dhcp/ directory, which supposedly contains the client lease database (HowTos)