Internet Fundamentals: How the Internet Actually Works

How the Internet Works

DNS, IP, routing, packets, transport, HTTP, CDNs, and how a page load crosses the global network.

What Is TCP/IP?

The protocol stack that powers the entire internet, explained from the ground up.

How TCP/IP Works

IP addressing, TCP reliability, UDP datagrams, ports, encapsulation, and how layers carry traffic.

TCP vs UDP

Why some traffic is reliable and ordered, and why some is fast and lossy — and when each is used.

TCP Slow Start and Congestion Control

Why TCP ramps up, backs off after loss, and depends so heavily on latency.

TCP Window Size

Receive windows, congestion windows, window scaling, and throughput limits.

The TCP Three-Way Handshake

SYN, SYN-ACK, ACK — how a connection is established and why it costs a round trip.

How a TCP Connection Closes

The four-way FIN exchange, half-close, TIME_WAIT, and FIN vs RST.

Bandwidth-Delay Product

Why a single connection to a distant server can't fill a fast link — and what window scaling fixes.

How HTTP Works

Requests, responses, headers, methods, and status codes — the protocol behind every web page.

What Are HTTP Headers?

The metadata on every request and response — Content-Type, Cache-Control, Cookie, and more.

HTTP Request Methods Explained

GET, POST, PUT, PATCH, DELETE, HEAD — plus the safe and idempotent rules behind retries.

What Are HTTP Cookies?

Set-Cookie and Cookie headers, session vs persistent, and the Secure, HttpOnly, and SameSite flags.

What Is CORS?

The same-origin policy, the preflight request, and why that CORS error appears in the console.

What Is a MIME Type?

How the Content-Type header tells a browser whether it has HTML, an image, or a download.

What Is URL Encoding?

Why URLs fill with %20 and %2F — percent-encoding, reserved characters, and double-encoding.

What Is a User Agent?

How to read the User-Agent string, why it all says Mozilla, and what client hints replace.

Content Encoding: Gzip vs Brotli

How Accept-Encoding negotiates HTTP compression — and why text shrinks 70–90%.

HTTP Status Codes Explained

1xx to 5xx — what each class means, the codes that matter for SEO, and client vs server errors.

HTTP vs HTTPS

What TLS adds to HTTP — encryption, integrity, and authentication — and why the lock icon matters.

How Email Works

SMTP, IMAP, MX records, SPF, DKIM, DMARC, queues, bounces, and mailbox sync explained.

HTTP/1.1 vs HTTP/2 vs HTTP/3

How the web protocol evolved from text-based requests to multiplexed QUIC streams.

What Is QUIC?

The UDP-based transport protocol behind HTTP/3 — and why it loads pages faster.

Head-of-Line Blocking

Why one stuck response stalls others — and how HTTP/2, HTTP/3, and QUIC address it.

How TLS Works

The handshake, certificates, and key exchange that secure your connection to every HTTPS site.

The TLS Handshake, Step by Step

ClientHello to Finished, message by message — and how TLS 1.3 cut it to one round trip.

What Is a Cipher Suite?

Reading a cipher suite string — key exchange, authentication, cipher, and hash.

Certificate Chains Explained

Root, intermediate, and leaf — how chains are built, validated, and why they break.

What Is a CSR?

The certificate signing request — what it contains and how it becomes a certificate.

What Is PKI?

How keys, certificates, CAs, and revocation fit together into a system of trust.

What Is Mutual TLS (mTLS)?

When both sides present certificates — client authentication and zero-trust networks.

OCSP vs CRL: Certificate Revocation

How a certificate is cancelled early — CRLs, OCSP, stapling, and why revocation is hard.

Perfect Forward Secrecy

Why a stolen server key can't decrypt yesterday's traffic — ephemeral key exchange.

What Is AES Encryption?

The block cipher behind almost all symmetric encryption — keys, rounds, and GCM mode.

What Is RSA Encryption?

Public-key cryptography built on the difficulty of factoring — encryption and signing.

What Is Diffie-Hellman?

How two parties agree on a shared secret over a public channel without sending it.

Elliptic Curve Cryptography

Why ECC gives the same strength as RSA with far smaller keys — ECDSA and ECDHE.

What Is End-to-End Encryption?

When only the endpoints hold the keys — versus encryption in transit and at rest.

What Is HMAC?

A keyed hash that proves both integrity and authenticity — used in API signing and tokens.

What Is a Salt in Hashing?

The random value that defeats rainbow tables and stops identical passwords from matching.

Certificate Authorities Explained

Root CAs, intermediates, certificate chains, and the trust model behind HTTPS.

Symmetric vs Asymmetric Encryption

Shared keys vs public/private key pairs, and why HTTPS uses both together.

Hashing vs Encryption

One-way fingerprints vs reversible secrecy — what a hash is, and why passwords are hashed.

How Digital Signatures Work

Hash then sign with a private key, verify with the public key — proving origin and integrity.

What Is HSTS?

How sites force HTTPS, the preload list, and the SSL-stripping attack it prevents.

Self-Signed Certificates

Why they can encrypt traffic but still trigger browser trust warnings.

SNI, ESNI, and ECH Explained

Why HTTPS can still reveal hostnames, and how Encrypted ClientHello reduces that leak.

What Is ICMP?

The protocol behind ping and traceroute — and why it occasionally gets blocked.

How VPNs Work

Encrypted tunnels, routing changes, DNS handling, protocols, speed impact, and leak risks.

What Is ARP?

How your device maps an IP address to a hardware MAC address on your local network.

What Is a MAC Address?

Hardware addresses, ARP, switches, randomized Wi-Fi addresses, privacy, and device identification.

How DNS Resolution Works

Root, TLD, and authoritative nameservers — the four-step lookup behind every domain you visit.

DNS Record Types Explained

A, AAAA, CNAME, MX, TXT, NS, and SOA — what each record does and when it is used.

What Is DNS TTL?

Why DNS changes take time to propagate, and how time-to-live values control caching.

DNS Poisoning Explained

How poisoned caches and spoofed answers can send users to the wrong address.

What Is a Hosts File?

Local hostname overrides, testing entries, and the risks of forgotten mappings.

mDNS and Bonjour Explained

How local devices discover names and services without a central DNS server.

Domain Name vs URL vs Hostname

The clean distinction between DNS names, hostnames, paths, and full URLs.

Domain Registration Explained

Registrars, registries, WHOIS, nameservers, renewals, transfers, privacy, and ownership basics.

What Is a TLD?

Top-level domains, registries, registrars, and where .com fits in DNS.

IPv4 Addresses Explained

The 32-bit address format, why we ran out, and how the four-octet system actually works.

IPv6 Addresses Explained

The 128-bit successor — hex notation, address types, and why adoption took two decades.

IPv6 SLAAC vs DHCPv6

How IPv6 devices get addresses from router advertisements, SLAAC, DHCPv6, or both.

IPv4 to IPv6 Transition

Dual stack, NAT64, tunnels, CGNAT, and why both protocols still coexist.

What Is a Loopback Address?

What 127.0.0.1, localhost, and ::1 mean when a device talks to itself.

Private vs Public IP Addresses

RFC 1918 ranges, why your home network uses 192.168.x.x, and how NAT bridges the two.

What Is NAT?

How one public IP address serves an entire household — and the four NAT types that affect gaming.

NAT Types Explained

Full cone, restricted, symmetric, Open, Moderate, Strict, CGNAT, and port forwarding.

What Is Double NAT?

Why two NAT layers break port forwarding, gaming NAT type, VPNs, and remote access.

NAT Traversal: STUN, TURN, ICE

How peers behind NAT connect directly — hole punching, relays, and the ICE framework.

CIDR Notation Explained

What /24 actually means, how subnet masks work, and how to read any CIDR block.

Subnetting Basics

CIDR, subnet masks, network IDs, broadcast addresses, and usable host counts.

How to Calculate a Subnet

A worked, step-by-step method — find the network, broadcast, host range, and count from any IP and mask.

VLSM Explained

Variable-length subnet masks — size each subnet to its need instead of wasting addresses.

What Is a Broadcast Address?

The all-ones host address, why it's the .255, and the difference from a multicast or unicast.

Special-Use IP Addresses

The reserved ranges — private, loopback, link-local, CGNAT — and what each is for.

IPv6 Address Types

Global unicast, link-local, unique local, and multicast — and why IPv6 dropped broadcast.

What Is a Port?

How one IP address handles dozens of services at once — and the well-known port numbers to know.

What Is a Network Socket?

IP plus port plus protocol — the endpoint behind every connection, and the 5-tuple that keeps them apart.

Common Port Numbers

The ports behind web, DNS, SSH, email, databases, remote access, and everyday troubleshooting.

How Internet Routing Works

How packets leave your network, cross ISPs, and reach websites through routing tables and BGP.

How Routing Works

How packets find their way across the internet through routing tables and BGP announcements.

What Is a Routing Table?

The next-hop lookup every device runs — entries, the default route, and longest prefix match.

BGP Explained

How autonomous systems announce routes and choose paths across the global internet.

What Is an Autonomous System?

ASNs, AS paths, transit and peering — the network-of-networks behind internet routing.

Interior vs Exterior Routing (IGP vs EGP)

OSPF routes inside a network by metric; BGP routes between networks by policy.

Static vs Dynamic Routing

Hand-configured routes versus protocols that learn paths automatically — and when each fits.

What Is a Default Route?

The 0.0.0.0/0 catch-all — the gateway of last resort for anything not matched elsewhere.

What Is OSPF?

The link-state interior protocol — areas, LSAs, the SPF algorithm, and cost-based paths.

What Is RIP?

The original distance-vector protocol — hop counts, the 15-hop limit, and why it aged out.

BGP Path Selection

How BGP picks one best path — local preference, AS-path length, MED, and the tie-breakers.

What Is MPLS?

Label switching, engineered paths, MPLS VPNs, and how it differs from the public internet.

BGP Hijacking Explained

Route leaks, prefix hijacks, RPKI, and what users notice when routing goes wrong.

What Is a Default Gateway?

The router that handles every packet leaving your local network — and what happens when it is wrong.

How Routers Work

Routing, NAT, DHCP, firewalls, Wi-Fi, switching, and why the router can become the bottleneck.

How a Network Switch Switches

MAC tables, forwarding, flooding, and the local delivery decisions inside a switch.

Collision vs Broadcast Domain

What each domain is, and how hubs, switches, and routers shape them.

Spanning Tree Protocol (STP)

How switches block redundant links to stop loops and broadcast storms.

What Is a VLAN?

Virtual LANs, trunk ports, access ports, subnet design, and network segmentation.

VLANs and Trunking

Access ports, trunk ports, 802.1Q tags, native VLANs, inter-VLAN routing, and common mistakes.

What Is a Broadcast Storm?

How a switching loop multiplies broadcasts into a meltdown — and how STP and storm control stop it.

What Is LLDP?

The layer-2 neighbor discovery protocol — how devices announce who and what they are.

What Is VXLAN?

Stretching a layer-2 network over layer 3 — the 24-bit overlay behind modern data centers.

Latency vs Bandwidth

Why high Mbps does not guarantee fast-feeling internet, and when ping matters more than speed.

Network Topologies Explained

Star, mesh, bus, ring, tree, and hybrid layouts for homes, offices, and provider networks.

Wi-Fi Standards Explained

Wi-Fi 4, 5, 6, 6E, 7, MIMO, OFDMA, QAM, bands, channel width, and real-world speed.

Wi-Fi Security Protocols

WEP, WPA, WPA2, WPA3, WPS, router security modes, and the safest home Wi-Fi settings.

The OSI Model Explained

All seven layers, what each one does, and how to use the model when troubleshooting.

The TCP/IP Model

The four-layer model the real internet uses — and how it maps to the seven-layer OSI reference.

Anatomy of an IP Packet

Headers, payloads, fragmentation, and what every field in a packet actually does.

Frame vs Packet vs Datagram

The clean mental model for frames, packets, segments, datagrams, and encapsulation.

What Is MTU?

Maximum packet size, Path MTU Discovery, VPN overhead, and why large packets can fail.

MSS vs MTU

The difference between total packet size and TCP payload size.

Jumbo Frames Explained

When 9000 MTU helps internal networks and why it is not an internet speed tweak.

How Traceroute Works

The TTL trick that reveals every router between you and a destination, hop by hop.

LAN vs WAN vs MAN vs PAN

The four network scales — from your Bluetooth earbuds to the entire internet.

Unicast, Multicast, Broadcast, Anycast

The four ways packets travel — to one host, many hosts, every host, or the nearest host.

Internet Connection Types

Fiber, cable, DSL, 5G home internet, fixed wireless, and satellite compared in practical terms.

Fibre Broadband Technologies

FTTP, GPON, XGS-PON, OLTs, ONTs, splitters, symmetric speeds, and fibre upgrade paths.

What Happens When You Type a URL

DNS lookup, TCP handshake, TLS handshake, HTTP request, render — every step demystified.

What Is a CDN?

How content delivery networks cache content close to you and make the web feel fast.

What Is Anycast?

How one IP address can serve users from the nearest data center automatically.

What Is a Proxy Server?

An intermediary that forwards your traffic — used for caching, filtering, and privacy.

Forward vs Reverse Proxy

Two opposite uses of the same idea — and why every major website is behind a reverse proxy.

HTTP Proxy vs SOCKS5

Protocol-aware web proxying compared with generic SOCKS5 forwarding.

What Is a Load Balancer?

How traffic is spread across many servers — and the difference between L4 and L7 balancing.

VPS vs Shared vs Dedicated

Hosting types compared by resources, control, cost, isolation, scaling, and responsibility.

What Is Edge Computing?

Why moving compute closer to users reduces latency and changes app design.