What is DNS? | How DNS works

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What is DNS? | How DNS works
What is DNS? | How DNS works

DNS (Domain Name System) is a hierarchical and distributed naming system that translates human-readable domain names into IP addresses.

It acts as a decentralized phonebook for the internet, allowing users to access websites, send emails, and perform other network-related activities using familiar domain names.

How DNS Works:

  1. User Enters a URL:
    • When a user enters a URL (e.g., www.example.com) into a web browser, the browser needs to find the corresponding IP address to connect to the server hosting that website.
  2. Local DNS Resolution:
    • The local device checks its cache (local DNS cache) to see if it already has the IP address for the requested domain. If found, the process skips the next steps.
  3. Recursive DNS Server:
    • If the IP address is not in the local cache, the device queries a Recursive DNS Server (also known as a resolver). The recursive server is responsible for finding the IP address by traversing the DNS hierarchy.
  4. Root DNS Servers:
    • If the recursive server doesn’t have the IP address, it starts the DNS resolution process from the root DNS servers. These servers are authoritative for the top-level domains (TLDs) like .com, .net, .org.
  5. TLD DNS Servers:
    • The root DNS server directs the recursive server to the TLD DNS server responsible for the specific top-level domain (e.g., .com). The TLD server, in turn, directs the resolver to the authoritative DNS server for the second-level domain.
  6. Authoritative DNS Server:
    • The authoritative DNS server holds the information about the IP address of the requested domain. It responds to the recursive server with the correct IP address.
  7. Response to the User:
    • The recursive server caches the IP address and sends it back to the user’s device. The device also caches the IP address for future use.
  8. Establish Connection:With the IP address, the user’s device can establish a connection to the server hosting the requested website or service.

How DNS works
How DNS works

 

How DNS works – Key Components of DNS:

  1. DNS Resolver:
    • Software or service on a user’s device or network that initiates DNS queries and caches the results.
  2. Root DNS Servers:
    • Thirteen authoritative servers at the top of the DNS hierarchy. They direct queries to the appropriate TLD DNS servers.
  3. TLD DNS Servers:
    • Servers responsible for specific top-level domains (e.g., .com, .org). They direct queries to the authoritative DNS servers for the second-level domains.
  4. Authoritative DNS Servers:
    • Servers that store and provide DNS information for a specific domain. They respond to queries with the IP addresses associated with domain names.

DNS Records:

  • A Record (Address Record):
    • Maps a domain to its corresponding IPv4 address.
  • AAAA Record:
    • Maps a domain to its corresponding IPv6 address.
  • CNAME Record (Canonical Name):
    • Alias of one domain to another.
  • MX Record (Mail Exchange):
    • Specifies mail servers responsible for receiving emails for a domain.
  • TXT Record (Text):
    • Contains arbitrary text, often used for DNS verification and authentication.
  • PTR Record (Pointer):
    • Used for reverse DNS lookups to map an IP address to a domain.

 

How DNS works – What are the steps in a DNS lookup?

For most situations, DNS is concerned with a domain name being translated into the appropriate IP address. To learn how this process works, it helps to follow the path of a DNS lookup as it travels from a web browser, through the DNS lookup process, and back again. Let’s take a look at the steps.

Note: Often DNS lookup information will be cached either locally inside the querying computer or remotely in the DNS infrastructure. There are typically 8 steps in a DNS lookup. When DNS information is cached, steps are skipped from the DNS lookup process which makes it quicker. The example below outlines all 8 steps when nothing is cached.

How DNS works – The 8 steps in a DNS lookup:

    1. A user types ‘example.com’ into a web browser and the query travels into the Internet and is received by a DNS recursive resolver.
    2. The resolver then queries a DNS root nameserver (.).
    3. The root server then responds to the resolver with the address of a Top Level Domain (TLD) DNS server (such as .com or .net), which stores the information for its domains. When searching for example.com, our request is pointed toward the .com TLD.
    4. The resolver then makes a request to the .com TLD.
    5. The TLD server then responds with the IP address of the domain’s nameserver, example.com.
    6. Lastly, the recursive resolver sends a query to the domain’s nameserver.
    7. The IP address for example.com is then returned to the resolver from the nameserver.
    8. The DNS resolver then responds to the web browser with the IP address of the domain requested initially.

Once the 8 steps of the DNS lookup have returned the IP address for example.com, the browser is able to make the request for the web page:

  1. The browser makes a HTTP request to the IP address.
  2. The server at that IP returns the webpage to be rendered in the browser (step 10).

In summary, How DNS works is a critical component of the internet infrastructure, translating human-readable domain names into machine-readable IP addresses, enabling seamless communication and access to online resources.

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