Understanding TCP/IP, HTTP, and Key Networking Concepts for Interviews

TCP operates at the transport layer of the TCP/IP model, providing reliable, connection‑oriented communication, while UDP offers a connection‑less alternative.

The TCP/IP stack consists of physical, link, network (IP, ARP, ICMP), transport (TCP, UDP), and combined session‑presentation‑application layers.

Typical interview questions include the TCP three‑way handshake (SYN, SYN‑ACK, ACK) and the four‑step connection termination (FIN, ACK, FIN, ACK).

HTTP is an application‑layer protocol that runs on top of TCP; each request creates a short‑lived, stateless TCP connection.

Common HTTP status codes are categorized as 2xx success (e.g., 200 OK), 3xx redirection (e.g., 301 Moved Permanently), 4xx client errors (e.g., 404 Not Found), and 5xx server errors (e.g., 500 Internal Server Error).

An HTTP message consists of a start line, header fields separated by CRLF, and an optional body whose length is indicated by the Content‑Length header.

When a user enters a URL, the browser performs DNS resolution, sends an HTTP request, follows redirects, receives the response, renders HTML, and subsequently requests embedded resources such as images, CSS, and JavaScript.