Whenever we connect to a service on the Internet, be it a website, a mail server, a remote terminal server, or any other service, we usually do so by invoking a domain name. In this article we will talk about the domain name system, or DNS (Domain Name System), and its operation. Now, every connection between us and any service in the network is carried out through a special type of socket called INET, or Internet. These sockets are composed of a 5-upla that identifies each of the connections between clients and servers.
What is a DNS Resolver
The DNS resolve or resolution of names on the Internet, is the relation between the name and a public IP address. This public IP is really what tells us where the website, mail server or other advanced parameters are located. To perform this conversion, private or public DNS servers are used, which indicate that IP has a specific domain name.
This DNS Resolver is done every time we make a query by name. Either to access a web page or send an email. If you look at your computer you have an internal IP address, but also 2 name resolution address IPs. These IPs are public servers of names that give the service of returning the public IP of the resource that we want.
Domain names work by associating a name or string with a specific termination to a public IP address to the Internet. In the same way that we give the name of the street and the number to get home, instead of giving the GPS coordinates. So in the case of domain names on the Internet would be street names and public IPs, the GPS coordinates.
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Types of DNS Resolutions
The iterative resolutions consist in the complete answer that the name server can give. The name server queries your local data (including its cache) looking for the requested data. The server in charge of making the DNS resolution iteratively asks the different DNS of the hierarchy associated with the name to be resolved, until descending into it to the machine that contains the authoritative zone for the name to be resolved.
In recursive DNS resolver, the server does not have the information in its local data, so it looks for and contacts a root DNS server, and if necessary repeats the same basic process (consult a remote server and follow to the next reference) until you get the best answer to the question.
When there is more than one authoritative server for a zone, Bind uses the lowest value in the RTT (round-time time) metric to select the server. The RTT is a measure to determine how long it takes a server to answer a query.
To Get the More info, visit: https://en.wikipedia.org/wiki/Domain_Name_System#DNS_resolvers