How do I renew my DHCP lease?
To renew your dhcp lease at the terminal:
sudo dhclient -r; sudo dhclient
In my case I had to specify which card to renew:
Note: you might want to join the two on one line, as otherwise you might lose the remote connection you're on after the first!
First release the current IP address:
sudo dhclient -r eth0
then renew the IP address
sudo dhclient eth0
.. or do them together to avoid losing connection:
sudo dhclient -r eth0 && sudo dhclient eth0
In the network drop-down selector from the system tray you can press the network you are already connected to, this will make network-manager ask for a new lease from a DHCP server.
(This also works for wired networks, but i don't think it works for PPP connections (mobile broadband))