Networking Interview Questions with Answers

7 layers (bottom to top): Physical (bits, cables), Data Link (frames, MAC, switches), Network (packets, IP, routers), Transport (segments, TCP/UDP), Session (connections), Presentation (encryption, compression), Application (HTTP, FTP, DNS). Mnemonic: "Please Do Not Throw Sausage Pizza Away".

TCP: connection-oriented, reliable (retransmission), ordered delivery, flow/congestion control. Slower. Used for: HTTP, email, file transfer. UDP: connectionless, unreliable, no ordering, no flow control. Faster. Used for: video streaming, gaming, DNS, VoIP. Trade-off: reliability vs speed.

(1) DNS resolution: browser → local cache → OS → DNS resolver → root → TLD → authoritative. (2) TCP handshake (SYN, SYN-ACK, ACK). (3) TLS handshake if HTTPS. (4) HTTP request sent. (5) Server processes request. (6) Response with HTML. (7) Browser parses HTML, loads CSS/JS, renders page.

HTTPS = HTTP + TLS. TLS handshake: (1) Client Hello (supported cipher suites), (2) Server Hello + certificate, (3) Client verifies certificate with CA, (4) Key exchange (asymmetric encryption for session key), (5) Both sides derive symmetric session key, (6) All subsequent data encrypted symmetrically. SSL is deprecated; TLS 1.3 is current.

DNS translates domain names to IP addresses. Resolution path: Browser cache → OS cache → Recursive resolver (ISP) → Root server (.com) → TLD server → Authoritative server (returns IP). Record types: A (IPv4), AAAA (IPv6), CNAME (alias), MX (mail), NS (nameserver). TTL controls caching duration.