When users typewrite domain names into the URL bar in the browser, DNS servers are accountable for translating the domain names to numeric IP addresses, directing them to the accurate website.
The Domain Name System (DNS) is the phone roster of the Internet. When users typewrite domain names like, let say, widespread one, ‘google.com’ or ‘nytimes.com’ into web browsers, DNS is accountable for obtaining the correct IP address for these websites. Browsers employ these addresses to interact with origin servers or CDN edge servers to locate website information. It all happens, thanks to DNS servers. These are the machines dedicated to answering DNS queries.
A server is a program or device devoted to rendering services to other applications, attributed to as ‘clients.’ DNS clients, which are developed into most advanced desktop and mobile working arrangements, facilitate web browsers to communicate with DNS servers.
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DNS servers resolve a DNS query
In a standard DNS query without any caching, four servers work collectively to give an IP address to the client:
- Recursive resolvers
- Authoritative nameservers
- Root nameservers
- TLD nameservers
The DNS recursor is also attributed to the DNS resolver. It is a server that accepts the query from the DNS client and later communicates with other DNS servers to track down the accurate IP. Once the resolver gets the request from the client, the resolver then acts as a client itself, investigating the supplementary three types of DNS servers in quest of the correct IP.
First, the resolver questions the root nameserver. The root server is the initial move in translating or resolving human-readable domain names into IP addresses. The root server then responds to the resolver with the address of a Top-Level Domain (TLD) DNS server (such as .com or .net) that stores the information for its domains.
Next, the resolver queries the TLD server. The TLD server acknowledges the IP location of the domain’s authoritative nameserver. The recursor then queries the authoritative nameserver, which will respond with the IP address of the origin server.
The resolver will finally pass the origin server IP address back to the client. Using this IP address, the client can then initiate a query directly to the origin server. The origin server will acknowledge by forwarding website data that can be evaluated and illustrated by the web browser.
In addition to the process outlined above, recursive resolvers can also resolve DNS queries using cached data. After retrieving the correct IP address for a proffered website, the resolver will save that information in its cache for a short amount of time. During this period, if any other clients send requests for that domain name, the resolver can skip the typical DNS lookup process and respond to the client with the IP address saved in the cache.
Once the caching time limit expires, the resolver must retrieve the IP address again, creating a new entry in its cache. This time limit referred to as the time-to-live (TTL), is set explicitly in the DNS records for each site. Typically the TTL is in the 24-48 hour range. A TTL is necessary because web servers occasionally change their IP addresses, so resolvers can’t serve the same IP from the cache indefinitely.
DNS servers may fail too
DNS servers can fail for multiple reasons, such as power outages, cyberattacks, and hardware malfunctions. In the early days of the Internet, DNS server outages could have a relatively significant impact. Thankfully, today there is a lot of redundancy built into DNS. For example, many instances of the root DNS servers and TLD nameservers, and most ISPs have backup recursive resolvers for their users. (Individual users can also use public DNS resolvers, like Cloudflare’s 18.104.22.168.) Most popular websites also have multiple instances of their authoritative nameservers.
In a significant DNS server outage, some users may experience delays due to the number of requests being handled by backup servers. Still, it would take a DNS outage of enormous proportions to make a significant portion of the Internet unavailable. (This happened in 2016 when DNS provider Dyn experienced one of the most powerful DDoS attacks in history). Cloudflare offers a Managed DNS Service that comes with built-in DNS security aimed at protecting DNS servers from attacks and other familiar sources of server failure.