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In my example, I used Google's DNS servers, so if you used my configuration, 
your hosts will first check your local server and then check Google's servers when 
resolving external names. Depending on your network hardware and configuration, 
you might even see a slight performance boost. This is because the DNS server you 
just set up is caching any lookups done against it. For example, if a client looks up 
https://www.packtpub.com
 in a web browser, your DNS server will forward the 
request along since that site doesn't exist locally and it will also remember the result. 
The next time a client within your network looks up that site, the response will be 
much quicker because your DNS server cached it.
To see this yourself, execute the following command twice on a node (device) that 
is utilizing your new DNS server:
dig www.packtpub.com 
In the response, look for a line toward the end that gives you your query time. It will 
look similar to the following:
;; Query time: 98 msec 
When you run it again, the query time should be much lower:
;; Query time: 1 msec 
This is your caching name server in action! Even though we haven't even set up 
any zone files to resolve your internal servers, your DNS server is already adding 
value to your network. You just laid the groundwork we'll use for the rest of our 
configuration.