How do you distinguish a DNS problem from a network problem?

If you're truly experiencing a DNS issue, your system will not be able to resolve host names (google.com) into IP addresses (74.125.225.78) which is what your computer really uses to communicate.

A simple test to verify that this is the case is to go to your terminal and ping a host name and then try to ping an ip address (on the internet). If you're able to ping the IP address and not the FQDN then you've got yourself a DNS issue because your DNS provider is not translating that name to an IP.

I suggest using either google DNS or OpenDNS, both of which are offered free of charge.

Here's the original answer by Ashlee:

go into your operating system command prompt and attempt to do a

nslookup for a domain such as google it should return a ip address

if it does not it is most likely a dns issue

to check for network issues use the ping command to ping a website and trace route command to trace the route to the ip address