Problem

A DevOps engineer supporting Meta infrastructure needs to explain DNS clearly, including what it does, how a lookup works, and why it matters for reliability and security.

Assume a user opens www.facebook.com from a browser. Explain what DNS does and walk through the request path from the client to the final IP address. Your answer should be practical, not purely academic.

Requirements

1. Define DNS and its primary purpose in IP networking.
2. Explain the difference between a domain name and an IP address.
3. Describe the main steps in DNS resolution, including:
   • local cache / OS resolver
   • recursive resolver
   • root nameserver
   • TLD nameserver
   • authoritative nameserver
4. Briefly explain common record types relevant to infrastructure work, such as A, AAAA, CNAME, and MX.
5. Describe why DNS is important for large-scale services like Facebook, Instagram, or WhatsApp, especially for service discovery, failover, and traffic routing.
6. Call out at least two security or operational risks involving DNS, such as spoofing, cache poisoning, misconfiguration, or TTL-related propagation issues.

Example prompt to answer

If a laptop inside Meta’s corporate network tries to reach www.facebook.com, what role does DNS play before any TCP or TLS connection is established?

What interviewers look for

A strong answer should show that DNS is a distributed naming system that maps human-readable names to machine-usable records, not just “a phonebook for the internet.” It should also connect DNS to real infrastructure concerns: caching, latency, redundancy, and security controls such as DNSSEC or resolver hardening.