IntermediatePhone
2 min
How DNS Resolution Works
DNSNetworkingWeb
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Interview Question
Walk me through the steps when you type a URL into your browser and press enter.
Key Points to Cover
- Browser cache lookup first
- OS resolver cache check
- Recursive DNS query to resolver
- Authoritative nameserver lookup
- Response cached and IP returned
Evaluation Rubric
Mentions local caches first25% weight
Explains DNS recursive resolver25% weight
Mentions authoritative nameservers25% weight
Describes IP returned to browser25% weight
Hints
- 💡Start with browser cache, end with IP resolved.
Common Pitfalls to Avoid
- ⚠️**Omitting Caching Layers:** Failing to detail the sequential checks in browser cache, HSTS cache, OS DNS cache, and the `hosts` file before initiating external DNS queries.
- ⚠️**Simplifying DNS Resolution:** Not clearly explaining the iterative nature of DNS resolution (resolver -> root -> TLD -> authoritative) or confusing recursive vs. iterative queries.
- ⚠️**Neglecting HTTPS/TLS Handshake:** Forgetting to mention the critical TLS/SSL handshake process for secure connections, especially given the prevalence of HTTPS.
- ⚠️**Skipping TCP Connection Establishment:** Overlooking the fundamental TCP three-way handshake that establishes the connection before any application-layer data (like HTTP requests) can be sent.
- ⚠️**Insufficient Detail on Rendering:** Merely stating 'the page loads' instead of elaborating on the browser's role in parsing HTML/CSS/JS, building the DOM, and making subsequent requests for embedded resources.
Potential Follow-up Questions
- ❓What’s the role of TTL?
- ❓How does DNSSEC fit in?
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