DNS resolver
On the Internet, any DNS resolver (alternatively known as Internet Service Provider's DNS resolver, ISP's DNS resolver, or, simply, resolver; hereinafter, the Resolver) is any server that (a) belongs to some Internet Service Provider and (b) moderates any process of translating (resolving) human readable hostnames into IP addresses that are used in communication between Internet hosts, or vice versa. The Resolvers are an essential part of Domain Name System (DNS).
The Resolvers receive requests in the form of a hostname from a web browser and request the needed data from root nameservers, which are the highest in the hierarchy, if the Resolvers haven't already cached that data. Indeed, the Resolvers not only redirect requests, but also cache the data needed to identify IP addresses.
Name-to-IP-address process
The complete name-to-IP-address process can be described in the following way:
- When the user enters a hostname (domain name) into a web browser, this browser queries their Resolver asking for the IP address.
- The Resolver asks the root nameserver where it can find details for that hostname, unless the resolver already has its IP address data cached.
- If it is asked, the root nameserver responds what TLD nameserver handles this data.
- The Resolver asks the TDL nameserver where it can find details for the entered hostname, unless it already has the data cached.
- If it is asked, the TLD nameserver responds that this data can be found at the host nameservers.
- The Resolver asks the host nameservers where it can find details for the needed IP address, unless it already has the data cached.
- If it is asked, the host nameservers have this data and respond with a DNS record containing the IP address for the entered hostname.
- The Resolver sends the identified data back to the web browser.
The name-to-IP-address process has been accomplished. Based on its results, the web browser points its request to the exact IP address in order to establish communication between this browser and that domain.
