The Domain Name System (DNS) is fundamental to the Internet. You use the DNS every time you do anything online including sending email and browsing the Web. Most networks use the DNS provided by their ISP or run their own small DNS server. OpenDNS is better.
"OpenDNS allows us to easily block unwanted sites and provide a safer, more productive environment. It has a smart interface that provides granularity of control across multiple connections, and the statistics are easy to use and provide insight into our DNS traffic."
— Terrell Johnson , Network Administrator , Sunsweet
$ sudo gedit /etc/dhcp3/dhclient.conf
# append the following line to the document
prepend domain-name-servers 126.96.36.199,188.8.131.52;
# save and exit
$ sudo ifconfig eth0 down && sudo ifconfig eth0 up
#note: in your system may not be 'eth0' for example in my PC it is eth1.