DNS stands for Domain Name System. The system translates domain names that are readable by people into IP addresses which the browser uses to load site pages.
Every device connected to the internet has a unique IP address that other devices use to find them. DNS servers allow people to use normal domain words that are easy to remember and write without having to recall every site´s IP address that are usually long and hard to type in (i.e IPV4 192.168.1.1)
How DNS works
As we´ve told earlier, DNS servers translate domain names into IP addresses. But how exactly do they do that?
When you make a search online, the URL you type goes through different servers to give the IP address.
- DNS recursor: also known as DNS resolver, receives the inquiry and contacts the other servers to find the correct IP address. These servers are operated by local networks, Internet Providers or third parties.
What the resolver does in first place is to look on the local cache for the hostname. If it finds it, it resolves the IP address immediately. If it doesn´t, then contacts the root DNS server and TLD nameservers. The TLD nameserver then receives details from an authoritative nameserver, asks for the requested hostname then matches it with the IP address, solving the request.
- Root DNS server: root servers are the first responsible to translate the domain to an IP address. These root servers answer different queries from other servers from the DNS. The root servers at first don´t know the IP address from the domain but do know where the nameservers that serve the domain are. After it finds the TLD server, it sends a query. Then the nameserver finds where the domain is stored and requests the IP address for that domain.
- TLD nameservers: these nameservers find the domain and request the IP address from an authoritative nameserver. This authoritative nameserver will contain the DNS records for the domain the user wants to search. Currently, there´s a specific nameserver for each TLD (Top Level Domain) like .com, .eu…
- Authoritative nameservers: this is the final part in the IP query. After the request, the authoritative nameservers checks if it has information from the domain and subdomain. Then check the DNS information and send the IP address to the DNS resolver.
With the DNS query resolved, the client gains access to the website or server and is able to communicate with it. The DNS will then be cached and remembered. That way the resolver directly gives the IP address of the searched domain when the client requests it.
What´s the difference between recursor and authoritative DNS?
After seeing how DNS works, it´s time to see what´s the difference between the recursor and authoritative DNS to better understand how it works.
Authoritative
Authoritative servers are in charge of connecting different domain names to their IP address. Think of them as the contact list on your phone, they find your contact´s name and then the number associated to that name to make a call.
They´re responsible for different regions like a certain local area or organization. These servers are also in charge of two very important jobs:
- To keep a record on the different TLD´s and IP addresses that those domains have
- The server is responsible of responding to requests from the recursor and the needed IP addresses from the domain names the client is trying to visit.
Recursive
As we´ve seen, the recursive server oversees receiving the URL from the search browser. It then checks the cache to see if it has the IP address from the domain. If not in the cache, the recursive DNS finds the IP address through the root, TLD or authoritative servers. Then saves it for a period of time called TTL (Time To Live).
This period of time is defined by the owner of the domain by setting a specific TTL.
To sum up this information, think of authoritative servers as the servers that keep the information of the IP addresses. While the recursive server acts as a mediator between the server and the client. It then courses through the DNS network to get the information from the authoritative server and the client.
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