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Junior

How does the Domain Name System (DNS) work?

sobes.tech AI

Answer from AI

DNS converts human-readable domain names (e.g., google.com) into IP addresses that computers use to identify each other on the network. The process involves several steps:

  1. Client query: The user enters a domain name into the browser.
  2. Recursive resolver: The browser sends a request to the local DNS resolver (usually the ISP's DNS server).
  3. Root DNS servers: If the resolver doesn't have the record in cache, it contacts the root DNS servers. The root server doesn't know the full IP but points to the TLD (Top-Level Domain) servers (e.g., for .com).
  4. TLD DNS servers: The resolver requests the TLD server, which points to the authoritative DNS servers for that domain.
  5. Authoritative DNS servers: The resolver contacts the authoritative server for the domain, which contains the exact record (e.g., A record for IPv4 or AAAA for IPv6), linking the domain name to an IP address.
  6. Resolver response: The authoritative server sends the IP address back to the recursive resolver.
  7. Caching and client response: The resolver caches the obtained IP address and sends it to the user's browser. The browser can now establish a connection to the server via the IP address.

Types of DNS records include:

  • A: Maps a domain name to an IPv4 address.
  • AAAA: Maps a domain name to an IPv6 address.
  • CNAME: Creates an alias from one domain name to another.
  • MX: Specifies mail exchange servers responsible for receiving email on behalf of a domain name.
  • TXT: Stores text strings, often used for verification (e.g., SPF, DKIM).
  • NS: Specifies the authoritative name servers for a domain.

Example of a step-by-step query:

// User requests google.com
// Browser asks local DNS resolver for google.com's IP
// Local resolver checks cache - not found
// Local resolver asks root server for google.com
// Root server says: "Ask .com TLD server"
// Local resolver asks .com TLD server for google.com
// .com TLD server says: "Ask Google's authoritative server"
// Local resolver asks Google's authoritative server for google.com
// Google's authoritative server says: "google.com is 172.217.160.142" (example IP)
// Local resolver caches 172.217.160.142 and sends it to the browser
// Browser connects to 172.217.160.142
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