Question 1

What is NAT (Network Address Translation)?

Accepted Answer

Translates private IP addresses to a public IP address, allowing multiple devices on a LAN to share a single public IP. Your router uses NAT: all devices in your home share one public IP. The router maps each outbound connection to a port number and translates replies back to the correct private device.

Question 2

What is a CDN (Content Delivery Network) and what problem does it solve?

Accepted Answer

A geographically distributed network of servers that serves content from the node closest to the user — reducing latency and origin load. Without CDN: all users hit your single origin server — slow for distant users, high load. With CDN: static assets (images, JS, CSS) are cached at edge nodes worldwide. Cloudflare, Akamai, and AWS CloudFront are popular CDNs.

Question 3

What is CORS (Cross-Origin Resource Sharing)?

Accepted Answer

A browser security mechanism controlling which cross-origin HTTP requests are allowed, based on server-sent headers. Same-origin policy blocks JS from making requests to a different origin. CORS lets servers opt-in: 'Access-Control-Allow-Origin: *' allows all origins. Preflight OPTIONS requests check permissions before complex requests.

Question 4

What is the difference between REST and GraphQL APIs?

Accepted Answer

REST uses fixed endpoints returning predefined data shapes; GraphQL uses a single endpoint where clients specify exactly what data they need. REST: GET /users/1, GET /users/1/posts — multiple round trips, may over/under-fetch. GraphQL: one query fetches exactly the fields you need. GraphQL adds complexity; REST is simpler and widely cached.

Question 5

What is the first thing that happens when you type a URL in a browser?

Accepted Answer

DNS resolution — the browser looks up the IP address for the domain name. Full flow: DNS lookup → TCP handshake → TLS handshake (for HTTPS) → HTTP request → server response → browser renders. DNS is always first. Results are cached locally to avoid repeated lookups.

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