Computer Networks Interview
Questions 2025

Physical, Data Link, Network, Transport, Session, Presentation, Application. Mnemonic: 'Please Do Not Throw Sausage Pizza Away'.

TCP: connection-oriented, reliable, ordered delivery (e.g., HTTP, FTP). UDP: connectionless, faster, no reliability guarantee (e.g., DNS, video streaming, gaming).

DNS resolution → TCP handshake → HTTP/HTTPS request → Server processes → HTML response → Browser renders. Full understanding impresses interviewers.

HTTP sends data in plaintext. HTTPS encrypts data using TLS/SSL. HTTPS uses port 443, HTTP uses port 80.

Subnet mask divides an IP into network and host parts. E.g., 255.255.255.0 (/24) gives 254 usable hosts. Subnetting splits a network into smaller sub-networks for efficiency.

Hub: broadcasts to all ports (Layer 1). Switch: sends to specific port by MAC (Layer 2). Router: routes between networks by IP (Layer 3).

DNS (Domain Name System) maps domain names to IP addresses. Flow: Browser cache → OS cache → Recursive resolver → Root nameserver → TLD → Authoritative nameserver.

SYN (client initiates) → SYN-ACK (server acknowledges) → ACK (client confirms). Establishes a reliable connection before data transfer.

ARP maps IP addresses to MAC addresses within a local network. A device broadcasts 'Who has IP X?' and the owner responds with its MAC address.

IPv4: 32-bit (4.3 billion addresses). IPv6: 128-bit (340 undecillion addresses). IPv6 solves address exhaustion and improves routing efficiency.

NAT allows multiple devices on a private network to share one public IP. The router translates private IPs to its public IP for outgoing traffic.

A firewall filters network traffic based on rules. Can block/allow by IP, port, protocol. Types: packet filter, stateful inspection, application-layer (proxy) firewall.