What is a DNS Server?
To put it simply, the Domain Name System (DNS) is the web’s address book. Domain Name System (DNS) is the service that locates the corresponding Internet Protocol (IP) address when a user enters a domain name like “google.com” or “nytimes.com” into a web browser.
The browser subsequently sends those addresses to the origin servers or CDN edge servers in order to retrieve the requested website data. DNS servers (computers set up specifically to respond to DNS inquiries) are responsible for making this possible.
What Is a Server?
An application or hardware server is one whose sole purpose is to serve other applications (called “clients”) with the resources they require. Web browsers are able to communicate with DNS servers because DNS clients are a standard part of the most contemporary desktop and mobile operating systems. Visit The Client-Server Model to learn more.
How do DNS Servers Resolve a DNS Query?
In a normal DNS query without caching, four servers (recursive resolvers, root nameservers, top-level domain (TLD) nameservers, and authoritative nameservers) collaborate to return an IP address to the client.
After receiving a query from a DNS client, the DNS precursor (also known as the DNS resolver) communicates with other DNS servers in an effort to locate the desired IP address. When a client makes a request, the resolver acts like a client and makes queries to the other three categories of DNS servers to find the correct IP.
The resolver begins its search by contacting the Internet’s primary nameserver. When converting domain names to IP addresses, the root server is used as the starting point.
In response to the resolver’s query, the root server provides the latter with the location of a specific top-level domain (TLD) DNS server (e.g.,.com or.net) that maintains data for that TLD.
The resolver then sends a query to the TLD server. Following a query to the TLD server, the authoritative nameserver for a domain will be returned as its IP address. After making a request to the primary nameserver, the precursor will receive the primary server’s IP address in response.
When the client requests the IP address of the original server, the resolver will give it to them. With this IP address in hand, the client can submit a request to the origin server, which will then give back the necessary website data for display by the user’s web browser.
What is DNS Caching?
Aside from the previously described method, recursive resolvers can also use cached information to quickly and efficiently answer DNS queries. Once the resolver has retrieved the proper IP address for a given website, it will keep that information in its cache for a predetermined amount of time.
If another client sends a request for that domain name during this time, the resolver can use the cached IP address to respond directly instead of performing a traditional DNS query.
The resolver will have to go out and get the IP address again, this time adding a new record to its cache, once the caching timeout has passed. The DNS entries for each website provide an explicit setting for how long each record is expected to remain valid, known as the time-to-live (TTL).
In most cases, the TTL will be between 24 and 48 hours. Because IP addresses assigned to web servers are dynamic, resolvers cannot continue to serve previously cached IP addresses indefinitely without a Time to Live (TTL) value.
What happens when DNS servers fail?
There are a number of potential causes of DNS server failure, including loss of power, malicious hacking attempts, and hardware failure. Prior to the development of backup mechanisms, DNS server failures might have serious consequences.
The Domain Name System (DNS) has, thankfully, been upgraded with a lot of redundancy in recent years. Most Internet service providers (ISPs) offer redundant recursive resolvers for their customers, and many copies of the root DNS servers and top-level domain nameservers are available.
(Personal computer users may also employ public DNS resolvers such as Cloudflare’s 220.127.116.11.) The authoritative nameservers of the most popular websites are usually replicated.
Some users may notice delays in the event of a severe DNS server failure because of the volume of requests being handled by backup servers, but it would take a massive DNS outage to render a significant percentage of the Internet inaccessible.
(In 2016, DNS provider Dyn was hit by one of the largest DDoS attacks ever recorded.) Cloudflare provides a Managed DNS Service with integrated DNS security to shield DNS servers from assaults and other common causes of server downtime.
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