Whenever you enter a web address into the browser’s search bar in the form of a URL (Uniform Resource Locator), a request is made to the resolver. This is a special component of the operating system that stores previously sourced IP addresses in a local cache and delivers them to client applications upon request. Should the desired IP address not be in the resolver’s cache, then the request is forwarded to the responsible DNS. Typically, this is the DNS server of your internet provider. There, the request is checked against the DNA database and the corresponding IP address is found (if there is one). This is known as ‘forward lookup’, and allows your browser to locate the desired web server via the internet. Alternatively, IP addresses can translate in the opposite direction, finding the respective domain name (‘reverse lookup’). If a DNS server is unable to answer a query from its existing database, it can collect the corresponding information from another database, or forward the request on to a different DNS server. These are known as recursive or iterative queries.
- Recursive: if the DNS server can’t answer the request itself, it can obtain the desired information from other servers. In this case, the resolver passes the DNS query onto the right DNS server. Once the domain name has been resolved, the answer is returned to the resolver.
- Iteration: In this instance, if the DNS server can’t answer the query, it simply returns the address of the next DNS server as an answer. The resolver must then send a new request to the next DNS server, and continue in this fashion until the domain name is resolved.
The central management of domain information in the DNS is characterized by high reliability and flexibility. Don’t worry if the server address is changed at the IP level, because the unchanged domain in the database will simply be allocated to the new IP address.