The Domain Name System (DNS) is a system of computers that holds computer or domain names and their associated Internet Protocol (IP) addresses. DNS resolving means that when a DNS server computer is asked, or queried, about a computer or domain name, it responds with an associated IP address. The process also works in reverse. When a reverse DNS lookup occurs, a DNS server is queried about an IP address and it responds with a name.
Two computers or network devices that are connected to the Internet or to another Internet Protocol (IP) based network must use numbers called IP addresses to communicate with each other. Humans remember names better than numbers, and therefore computers are given names as well. DNS resolving works behind the scenes by letting people use names to find network resources instead of trying to remember complex IP addresses.
If a person types a web address into the address bar at the top of their browser and clicks go, the computer will immediately ask the DNS server belonging to the Internet Service Provider (ISP) for the IP address to contact that website. The DNS server will respond with an IP address associated with a web server computer of the desired website. Then, the user computer utilizes the returned IP address to send a default web page request directly to the desired website's web server.
In some cases, web browsers are programmed by their manufacturers to contact a computer belonging to a search provider, no matter what gets typed in the address bar. In this situation, the address bar is being used for a web search. The computer will then query a DNS server for the IP address to a machine associated with a search provider.
DNS resolving is often used with network tools, email tools, and for Internet security. For instance, a person can open a command prompt or terminal window and type ping [desired website address]. When the user presses enter, a request will be sent to a DNS server to convert the website address into an IP address. The ping utility will then ask the machine with that IP address to reply.
DNS servers are connected together in a hierarchy of domains. If a local DNS server is queried about a name or IP address it does not know about, the DNS server will forward the request to a higher level DNS server. This request forwarding will continue until a name is found or it is established that the name does not exist.
Without DNS forwarding, people would have a very difficult time using the Internet. Hyperlinks use domain or website names to find things. This helps to ensure that the Internet remains user friendly. If everyone had to use IP addresses instead of names, the Internet would have never been publicly accepted and may have ceased to exist.