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Computer Networks & OS Intermediate Level ~3 min read

What happens step-by-step during a DNS Lookup when typing a URL into the browser?

Quick Revision Summary

DNS lookup traverses browser cache → OS cache → Recursive resolver → Root server → TLD server → Authoritative server, translating domain names to IP addresses over UDP port 53.

Interactive Practice Mode
Formulate your thoughts or take notes before revealing the model solution.
Model Answer & Deep-Dive Explanation

When a user requests https://freshershome.com, the DNS resolution follows this hierarchical sequence:

  1. Browser DNS Cache: Checks local browser cache for a recent TTL record.
  2. OS Resolver & Hosts File: Checks operating system DNS cache and /etc/hosts file.
  3. Recursive DNS Server (ISP / Cloudflare 1.1.1.1 / Google 8.8.8.8): If cache misses, the OS queries the recursive resolver.
  4. Root Name Server (.): The recursive resolver contacts one of 13 global root clusters to locate the Top-Level Domain server for .com.
  5. TLD Name Server (.com): Points the resolver to the authoritative nameservers for freshershome.com.
  6. Authoritative Name Server: Holds the official zone file and retu s the A (IPv4) or AAAA (IPv6) record.
  7. Caching & Connection: The resolver caches the IP with its TTL, retu s it to the OS and browser, which then initiates the TCP 3-way handshake and TLS negotiation.

Interviewer Evaluation Points & Scoring Rubric

  • 1 1. Details all stages of DNS hierarchy. 2. Distinguishes recursive resolver from authoritative server. 3. Mentions caching, TTL, and UDP port 53.
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