What is DNS?
DNS is essentially a translator between what people want and what a network needs to make that happen. People, for the most part, understand text names of hosts and services—for instance, google.com or paypal.com. However, these names don't mean anything to the underlying network. What DNS does is take those "fully qualified hostnames" that someone might type into an application, such as their browser at Open Systems Interconnection (OSI) Layer 7 (remember the OSI layers in Chapter 3, Using Linux and Linux Tools for Network Diagnostics), and translates them into Internet Protocol (IP) addresses that can then be used to route the application request at OSI Layers 3 and 4.
In the reverse direction, DNS can also translate an IP address into a fully qualified domain name (FQDN), using what's called a pointer (PTR) request (for a DNS PTR record) or "reverse lookup". This can be important to technical folks, but these requests are not...
