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Merge pull request #63 from codeharborhub/dev-1
Docs: started new docs for Internet Topic
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‎docs/internet/browser-devtools.mdx‎

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<ComingSoon />

‎docs/internet/cdn.mdx‎

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<ComingSoon />

‎docs/internet/clients-and-servers.mdx‎

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---
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title: "Clients and Servers"
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description: "Understand how clients and servers form the backbone of the Internet — how requests and responses flow, what roles each plays, and how they communicate using protocols."
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tags: [internet, client-server, networking, web, protocols]
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sidebar_label: Clients & Servers
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---
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The Internet operates on a simple yet powerful concept: **clients and servers**. Every time you browse a website, watch a video, or send an email, your device (the *client*) communicates with another system (the *server*) that provides the requested data or service.
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## The Core Idea
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Think of the Internet as a giant conversation. Your computer, phone, or browser **asks questions** and servers **reply with answers**.
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In this model:
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* The **client** initiates communication.
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* The **server** listens, processes, and responds.
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## What Is a Client?
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A **client** is any device or software that requests resources or services from a server.
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Common examples:
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* Web browsers (like Chrome, Firefox, Edge)
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* Mobile apps
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* Command-line tools (like `curl` or `wget`)
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Clients don’t store the data permanently, they only display or use it temporarily.
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```mermaid
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graph TD
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A[User - Client] -->|Request| B[Server]
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B -->|Response| A
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```
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## What Is a Server?
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A **server** is a system (computer or application) that **stores**, **manages**, and **serves** data to clients over a network. It runs specialized software like:
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* **Web servers** (e.g., Apache, Nginx)
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* **Database servers** (e.g., MySQL, MongoDB)
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* **Mail servers** (e.g., Postfix)
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Servers are designed for **reliability** and **availability**, often running 24/7 in data centers.
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## How Clients and Servers Communicate
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Communication follows a **request-response model**, using **protocols** such as HTTP or HTTPS.
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1. The client sends a **request** to a server.
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2. The server **processes** the request.
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3. The server sends a **response** (like an HTML page or JSON data).
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Here’s a simplified example:
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```http
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GET /home HTTP/1.1
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Host: codeharborhub.github.io
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```
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The server replies:
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```http
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HTTP/1.1 200 OK
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Content-Type: text/html
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<html>
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<body>Welcome to CodeHarborHub!</body>
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</html>
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```
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## Real-World Example
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When you visit **https://codeharborhub.github.io**:
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* Your browser (the client) sends a request.
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* GitHub Pages (the server) finds and returns the website files.
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* The browser displays them on your screen.
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You never directly see the server, but every webpage you view comes from one.
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## Types of Client–Server Architecture
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| Type | Description | Example |
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|------|--------------|----------|
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| **1-Tier** | Client and server on the same machine | Local software like MS Word |
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| **2-Tier** | Direct client-server communication | Web browser ↔ Web server |
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| **3-Tier** | Includes a database layer | Browser ↔ App server ↔ Database |
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| **N-Tier** | Distributed services and APIs | Modern cloud-based systems |
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## Security & HTTPS
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When data travels between client and server, security is essential. With **HTTPS**, information is encrypted using **SSL/TLS**, preventing eavesdropping and tampering.
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```mermaid
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sequenceDiagram
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participant Client
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participant Server
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Client->>Server: Request (HTTPS)
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Server-->>Client: Response (Encrypted)
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```
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## Key Takeaways
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* **Clients** request data or services.
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* **Servers** store and deliver that data.
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* They communicate through **standard protocols** (HTTP, HTTPS, FTP, etc.).
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* The **request–response model** is at the heart of how the Internet works.
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* Modern systems often involve **multiple servers and APIs** behind the scenes.
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> “Every click, every page, every message you send, is just one client talking to one server somewhere in the world.”

‎docs/internet/dns.mdx‎

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---
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title: "Domain Name System (DNS)"
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description: "Explore the Domain Name System (DNS) — the backbone of the Internet that translates human-readable names into IP addresses. Learn its structure, types of records, and how the DNS resolution process works."
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tags: [dns, networking, internet, domain, ip, infrastructure]
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sidebar_label: DNS
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---
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The **Domain Name System (DNS)** is one of the most essential — yet often overlooked components of the Internet. It’s what allows us to use memorable names like `codeharborhub.github.io` instead of complex numerical IP addresses.
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DNS acts as the **Internet’s phonebook**, translating **domain names** into **IP addresses** so browsers can locate and communicate with servers worldwide.
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## Why DNS Exists
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Computers communicate using numbers (IP addresses), not words. Before DNS, users had to manually look up and remember numeric addresses — an unscalable and error-prone process.
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DNS was created to solve this by introducing a **distributed, hierarchical naming system** that’s:
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* **Human-friendly**: You type names, not numbers.
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* **Scalable**: Works across billions of domains.
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* **Automatic**: Queries happen invisibly in milliseconds.
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## DNS Hierarchy Overview
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The DNS system is hierarchical, like a tree:
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```mermaid
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graph TD
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A[Root Zone - .] --> B[Top-Level Domains - .com, .org, .io]
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B --> C[Second-Level Domains - example.com]
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C --> D[Subdomains - blog.example.com]
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D --> E[Hostnames - www, mail]
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```
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Each level plays a specific role in locating resources on the Internet.
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## How a DNS Query Works (Step-by-Step)
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When you enter a URL such as **https://codeharborhub.github.io**, your browser performs several steps to find its IP address:
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```mermaid
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sequenceDiagram
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participant User
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participant Browser
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participant Resolver
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participant RootServer
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participant TLDServer
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participant AuthoritativeServer
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User->>Browser: Enter codeharborhub.github.io
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Browser->>Resolver: Request IP address
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Resolver->>RootServer: Ask for .io TLD info
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RootServer-->>Resolver: Return .io TLD name servers
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Resolver->>TLDServer: Ask for github.io info
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TLDServer-->>Resolver: Return authoritative server
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Resolver->>AuthoritativeServer: Ask for codeharborhub.github.io
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AuthoritativeServer-->>Resolver: Return IP address
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Resolver-->>Browser: 185.199.108.153
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Browser->>185.199.108.153: Send HTTP Request
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```
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All this happens in a fraction of a second.
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## The Four Key DNS Server Types
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| Server Type | Description |
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|--------------|--------------|
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| **DNS Resolver (Recursive Resolver)** | Usually provided by your ISP or a public DNS service (like Google `8.8.8.8`). It initiates and manages DNS lookups on your behalf. |
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| **Root Name Server** | The top-level of DNS — knows where to find TLD servers (like `.com`, `.io`, `.net`). |
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| **TLD Name Server** | Stores information about domains under a specific top-level domain. |
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| **Authoritative Name Server** | The final authority — provides the actual IP address for a domain. |
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## Common DNS Record Types
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DNS uses **resource records (RRs)** to store information. Each type serves a specific purpose:
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| Record Type | Description | Example |
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|--------------|--------------|----------|
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| **A** | Maps a domain to an IPv4 address. | `codeharborhub.github.io → 185.199.108.153` |
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| **AAAA** | Maps a domain to an IPv6 address. | `example.com → 2606:2800:220:1:248:1893:25c8:1946` |
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| **CNAME** | Alias for another domain name. | `www.example.com → example.com` |
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| **MX** | Mail server record (used for email routing). | `example.com → mail.example.com` |
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| **TXT** | Stores arbitrary text info (SPF, DKIM, verification). | `v=spf1 include:_spf.google.com ~all` |
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| **NS** | Identifies the authoritative name servers for a domain. | `example.com → ns1.example.net` |
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## DNS Caching — Speed Optimization
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To reduce lookup time and network load, DNS results are **cached** at multiple levels:
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* **Browser Cache** – Short-term memory for recently visited domains.
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* **Operating System Cache** – Local DNS records stored temporarily.
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* **Resolver Cache** – Managed by ISPs or public DNS resolvers.
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Each record has a **TTL (Time To Live)** that defines how long it stays valid before a recheck.
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## Practical Example — DNS Lookup Flow
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<Tabs>
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<TabItem value="nontechnical" label="Simple View" default>
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You type `codeharborhub.github.io` → DNS finds its IP → Browser connects → Website loads.
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It’s that simple — all automatic.
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</TabItem>
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<TabItem value="technical" label="Technical Flow">
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1. The browser checks its cache.
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2. If not found, it asks the **local resolver**.
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3. The resolver queries **root**, **TLD**, and **authoritative** servers.
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4. The IP is returned and cached.
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5. The browser sends the HTTP request to that IP.
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</TabItem>
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</Tabs>
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## DNS in Action — Simulation
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```jsx live
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function DnsDemo() {
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const [resolved, setResolved] = React.useState(false);
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const resolve = () => setResolved(true);
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return (
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<div style={{ textAlign: "center" }}>
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<h3>DNS Resolution Simulation</h3>
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<p>Domain: codeharborhub.github.io</p>
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<button onClick={resolve}>Resolve Domain</button>
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{resolved && <p> IP Address: 185.199.108.153</p>}
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</div>
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);
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}
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```
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## Security in DNS
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DNS was designed for speed and reliability — not security. Attackers exploit this through methods like:
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* **DNS Spoofing / Cache Poisoning:** Injecting false IP mappings.
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* **DNS Hijacking:** Redirecting users to malicious servers.
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* **Amplification Attacks:** Overloading DNS servers to cause downtime.
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To counter these, **DNSSEC (Domain Name System Security Extensions)** was introduced. It digitally signs DNS data, ensuring authenticity and integrity.
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## Key Takeaways
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* DNS is the **Internet’s distributed naming system** that maps domain names to IP addresses.
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* The DNS hierarchy consists of **Root**, **TLD**, and **Authoritative** servers.
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* DNS uses various **record types** (A, AAAA, CNAME, MX, TXT) to manage different data.
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* **Caching** makes DNS fast, while **DNSSEC** makes it secure.
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* Every click, website, or API request starts with a DNS lookup — it’s the silent foundation of the web.
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:::tip
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Learn about [IP Addressing](./ip-addresses.mdx) — the numerical system that identifies every device on the Internet.
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:::

‎docs/internet/firewalls.mdx‎

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<ComingSoon />

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