Instead of killing the process in order to run dhclient to get a new lease, just release it. See? No need to kill it. Now you can ask for another lease.

See current network properties for all interfaces, Manually configure an IP address for interface eth0, See the current network properties for all wireless interfaces, Configure wireless to talk to a specific access point by address, Configure a wireless interface to use channel 11, Set the default gateway, Configure static routes, See what PIDs/processes are associated with remote connections