For those burned by the latest internet carrier outage, try adding an alternate DNS server to your resolv.conf (or its equivalent in other operating systems). This will solve problems faced by some ISP's DNS servers.
For example, OpenDNS provides a great free service. Their servers are:
184.108.40.206 and 220.127.116.11
If you are using DHCP to populate resolv.conf, remember to update the dhclient.conf file. For example,
prepend domain-name-servers 18.104.22.168;
Add this to the dhclient.conf file of the network interface you are using. For example, for eth0, the file will be /etc/dhclient-eth0.conf
While you are at it, consider running a local DNS caching server on your machine. This will result in a quicker network access for you, and also reduce the load on the public DNS servers. For example, dns-masq is a great and easy to use DNS caching server.
To make sure your local DNS server is used, add another line to dhclient.conf as follows:
prepend domain-name-servers 22.214.171.124; prepend domain-name-servers 127.0.0.1;