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Networking Interview Questions — What Senior Engineers Need to Know

Networking fundamentals underpin every distributed system and web application. Senior engineers are expected to understand not just what TCP does, but how the three-way handshake works, why Nagle’s algorithm exists, and what actually happens when you type a URL into a browser.

These 13 questions cover the networking concepts most relevant to backend and full-stack interviews: protocol differences, connection lifecycle, DNS resolution, TLS handshakes, and HTTP/2 improvements. Understanding these deeply helps you debug production issues and make informed architectural decisions.

All 13 Questions

TCP — 3-Way HandshakeExplain the TCP 3-way handshake.TLS — Certificate, DH, AESHow does TLS work? Explain certificates, Diffie-Hellman, and AES.TCP vs UDPWhat is the difference between TCP and UDP?HTTP vs HTTPSWhat is the difference between HTTP and HTTPS?WebSocketsWhat are WebSockets and when would you use them instead of HTTP?REST vs gRPCWhat is the difference between REST and gRPC?OSI LayersWhat are the 7 OSI layers and what does each do?CORS + PreflightWhat is CORS and how does the preflight request work?HTTP/1.1 vs HTTP/2 vs HTTP/3What are the key differences between HTTP/1.1, HTTP/2, and HTTP/3?HTTP Request StructureWhat is the structure of an HTTP request?HTTP Status CodesWhat are the main HTTP status code categories and key codes?HTTP Methods — IdempotencyWhich HTTP methods are idempotent and why does it matter?GraphQL vs RESTWhat are the differences between GraphQL and REST?

How to Prepare

Focus on understanding concepts deeply enough to explain them in your own words. For each topic, practice articulating the trade-offs and real-world applications — interviewers care about practical judgment, not textbook definitions.

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