It is very important to ensure your
/etc/resolv.conf file is configured with proper nameservers in order for DNS resolution to function correctly on your host. What should these values be set to?
You should reach out to your web hosting provider or systems administrator to determine what nameservers should be used in this file. However, you can default to using Google's nameservers if you are uncertain or are in a hurry to get them working properly:
[root@host]# grep nameserver /etc/resolv.conf
If you are uncertain of how to edit this configuration, please see the following article.