66 Essential Computer Network Concepts Every Developer Should Know

Overview of Computer Network Knowledge

Computer networking fundamentals are frequently tested in interviews and are essential in daily development work. This article compiles 66 important concepts, ranging from HTTP protocol versions and request methods to TCP/IP mechanics, TLS/HTTPS security, performance optimization, caching, cookies, tokens, and security threats.

1. Comparing HTTP 0.9 and HTTP 1.0

HTTP 0.9 is a minimal protocol with only a GET method, no headers, and a single request‑response round‑trip. HTTP 1.0 adds headers, status codes, redirects, errors, conditional requests, and content encoding, requiring two round‑trips.

Client builds request → DNS lookup → TCP three‑way handshake → request → server response → TCP four‑way termination (single round‑trip for HTTP 0.9, two for HTTP 1.0).

2. HTTP 1.1 and HTTP 2

HTTP 1.1 introduces persistent connections, caching header extensions, OPTIONS, Upgrade, Range requests, compression, and pipelining, but still suffers from head‑of‑line (HOL) blocking. HTTP 2 solves HOL blocking with binary framing, multiplexing, header compression, stream prioritization, server push, flow control, and reset messages.

Using HTTP 2 reduces perceived latency and improves TCP connection utilization.

3. Common HTTP Request Methods

GET

– retrieve resources. POST – submit data to a resource. PUT – update or replace a resource (specifies the target location). HEAD – fetch only headers. DELETE – remove a resource. OPTIONS – list supported methods (e.g., GET,POST). TRACE – echo the received request for debugging. CONNECT – convert the request connection to a tunnel (used by proxies).

4. From URL Input to Page Rendering

The browser resolves the domain via DNS, establishes a TCP connection, performs TLS handshake if needed, sends the HTTP request, receives the response, parses HTML, builds the DOM, discovers resources, queues them, and finally renders the page. Rendering involves a rendering engine (layout, paint) and a JavaScript engine (execution).

5. Web Performance Optimization

Key performance factors include data packets, latency, bandwidth, connection‑establishment time, and TCP three‑way handshake. Optimizations cover DNS query caching, client‑side caching, TCP connection reuse, avoiding redirects, edge caching, conditional caching, compression, code minification, and image optimization.

Metrics such as TTFB (time to first byte), content download time, start‑render time, and document load completion are used to evaluate performance.

6. HTTP 2 Technical Details

HTTP 2 uses a binary framing layer where each frame has a 9‑byte header (length, type, flags, reserved bit, stream identifier) followed by a variable‑length payload. Frames are interleaved across streams, allowing out‑of‑order delivery and reassembly based on stream IDs.

Multiplexing eliminates the need for multiple TCP connections, reducing HOL blocking.

7. HTTPS and TLS

HTTPS adds SSL/TLS encryption to HTTP, providing confidentiality, integrity, and authentication. The handshake involves the client sending supported cipher suites and a random value, the server responding with a certificate and its random value, the client verifying the certificate, generating a pre‑master secret encrypted with the server’s public key, and both sides deriving symmetric keys for bulk encryption.

Certificates are issued by Certificate Authorities (CAs) after verification, and the signature is created by hashing the certificate data and encrypting the hash with the CA’s private key.

8. Cookies, Sessions, and Tokens

Cookies store small key‑value pairs on the client to maintain state across HTTP’s stateless requests. Attributes include domain, path, expiration, HttpOnly, Secure, and SameSite (Strict, Lax, None). Sessions store state on the server, identified by a session ID usually stored in a cookie. Tokens (e.g., JWT) provide stateless authentication, reducing server load.

9. Security Threats: CSRF and XSS

CSRF exploits a logged‑in user's credentials to perform unwanted actions; defenses include SameSite cookies and anti‑CSRF tokens. XSS injects malicious scripts into pages; mitigation involves output encoding, Content‑Security‑Policy, and HttpOnly cookies.

10. Caching Strategies

Strong (browser) caching uses Expires and Cache‑Control headers (e.g., max‑age, public, private, no‑cache, no‑store). Conditional caching uses ETag and Last‑Modified headers, allowing the server to respond with 304 Not Modified when resources are unchanged.

11. TCP/IP Basics

TCP is a connection‑oriented, reliable, byte‑stream protocol with flow control, congestion control (slow start, congestion avoidance, fast retransmit, fast recovery), and sequence/acknowledgment numbers. UDP is connection‑less, unordered, and faster but unreliable.

TCP three‑way handshake establishes a connection (SYN, SYN‑ACK, ACK). Four‑way termination gracefully closes it (FIN, ACK, FIN, ACK).

12. DNS Resolution Process

Clients query recursive resolvers, which traverse the DNS hierarchy: root → TLD → authoritative name servers, ultimately returning the IP address for the requested domain.

13. HTTP Headers Overview

Key request headers: Accept, Accept‑Encoding, Accept‑Language, Accept‑Charset, Cookie, Range. Key response headers: Content‑Type, Content‑Encoding, Content‑Length, Content‑Range, Set‑Cookie, Cache‑Control, Expires, ETag, Last‑Modified, Transfer‑Encoding, Connection, Location, Allow.

14. HTTP Status Codes

Informational (1xx), Success (2xx), Redirection (3xx), Client Error (4xx), Server Error (5xx). Examples: 100 Continue, 200 OK, 201 Created, 301 Moved Permanently, 302 Found, 304 Not Modified, 401 Unauthorized, 403 Forbidden, 404 Not Found, 500 Internal Server Error, 503 Service Unavailable.

15. HTTP/3 and QUIC

HTTP/3 runs over QUIC, a UDP‑based transport that provides multiplexed streams, reduced connection latency (0‑RTT), and built‑in encryption. QUIC eliminates TCP’s HOL blocking and improves loss recovery by allowing independent stream retransmission.

16. Practical Interview Questions

Explain the differences between HTTP 1.0, 1.1, 2, and 3.

Describe the TCP three‑way handshake and four‑way termination.

List common HTTP methods and when to use them.

What are cookies, sessions, and tokens? How do they differ?

How do CSRF and XSS attacks work and how can they be mitigated?

Explain caching mechanisms (strong vs. conditional).

What is the purpose of the Accept header?

Describe the role of TLS in HTTPS.

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