Computers on the Internet are identified by two names. One is the domain name, a human-friendly address, and the other is the Internet Protocol, or IP, address, consisting of a series of numbers. For instance, you can either type "google.com" or "74.125.224.72" into a Web browser and get to the same Web page. Your computer connects to a Domain Name Service server that translates domain names into IP addresses. If there are issues with the DNS server, then you'll have problems getting online. If you're using the Ubuntu distribution of Linux, clearing up any issues with DNS takes a little knowledge of networking and some troubleshooting.
Check Network
First, make sure your network is running properly. Power-cycling your router and modem can sometimes resolve minor networking issues. Unplug your modem, and then unplug your router, if you're using one. Wait 30 seconds, plug in your router, and then plug in your modem. If that still doesn't fix the DNS issue, call your Internet service provider to find out if it is having a DNS outage. If it is, most times its DNS server will be back up and running quickly, or it will be able to provide a backup DNS server to use.
Editing DNS Servers
If your ISP isn't having a problem with its DNS servers, then double-check your network settings. Make sure you have the DNS servers and domains your ISP wants you to use. If you're unsure, call your ISP for the IP addresses. In the system tray, right-click on the Network Manager icon and pick "Edit Connections." Click on the connection you're using. If you're using a wired connection, it will be under the Wired tab, while a wireless connection will be under the Wireless tab. Click the "Edit" button and choose the "IPv4 Settings" tab. For "Method," pick "Automatic (DHCP) addresses only." List the DNS servers by their IP addresses separated by a comma in the "DNS Servers" box. Then type the domain name from your ISP under "Search Domains." Finally, click "OK."
Resolv.conf
The resolv.conf file in your /etc directory holds the addresses for your DNS servers. Periodically this can be overwritten by accident, so you might have to add the servers back in by hand. Using the DNS servers and domain names supplied by your ISP, add them to "/etc/resolv.conf" as root or with sudo. Be sure to use a text editor, such as gedit, vim or emacs, and not a word processor, since a word processor will add extra characters to the file and cause problems. The first line of resolv.conf should be "domain" followed by the domain name. Under the domain line should be your DNS servers written as "nameserver" followed by the IP address of the DNS server. Most times, your ISP will give you a primary DNS server, followed by a secondary, or a backup server. If you have a secondary DNS server, it should be on its own line, just as you added the first DNS server. Don't forget to save the file before exiting the text editor.
Different Network Manager
Sometimes different network managers work better with certain network adapters. A basic network manager to try is Wicd, although it doesn't have all the features of the default Gnome Network Manager. You'll need to uninstall "network-manager" and "gnome-network-manager" either through apt or Synaptic. Once you've installed Wicd, start it by clicking on it under "Applications" and "Internet." Wired networks should be automatically detected, and you'll have to choose the wireless network from the list.
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