DHCP allows machines on an IP-based network to automatically obtain configuration information such as IP addresses, subnet masks, router addresses, etc.

If a machine is connected to a network and has received the above-mentioned configuration settings but is unable to access other machines or the Internet, you might need to renew its DHCP lease.

To do this, open a Terminal window and enter this command to remove the current configuration settings:

sudo dhclient -r

… followed by this command to renew them:

sudo dhclient

If the machine is still unable to connect, you can try disabling and re-enabling the network interface:

sudo ifdown eth0
sudo ifup eth0

… or restarting the network service (try either of the commands below):

sudo /etc/init.d/network restart
sudo /etc/init.d/networking restart

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