vault backup: 2025-04-12 23:43:56

Affected files:
.obsidian/workspace.json
Kuwait University Masters Prep

Author: Cyberistic

4 - Network and Security/10 - Principles of network applications.md

@@ -1 +1,133 @@
-(HTTP, Electronic Mail, DNS)
+Principles of network applications and its protocols (HTTP, Electronic Mail, DNS).  
+
+Super vague description, will provide general knowledge about the above.
+
+
+
+##🌐 What is the internet?
+
+Network applications let devices **communicate over the internet**. These applications (like web browsers, email clients, or video apps) rely on **application-layer protocols** that define how data is sent and received.
+
+Unlike lower layers (like TCP/IP or Ethernet, which will be discussed in the next notes), the application layer is what users interact with directly.
+
+---
+
+## 💬 Application Architecture
+
+Two main types of communication structures:
+
+- **Client-Server Model**
+    
+    - One central **server** responds to many **clients**.
+        
+    - E.g., web servers and browsers.
+        
+- **Peer-to-Peer (P2P) Model**
+    
+    - Devices (peers) both request and provide services.
+        
+    - E.g., file sharing like BitTorrent.
+
+
+> [!Important] Fun fact..
+> [Tailscale](https://tailscale.com/) allows you to establish a P2P connection by using their service as the server for the initial "handshake" only.
+> I've used it recently as a VPN
+
+
+
+## 📡 Key Application Protocols
+
+### 1. **HTTP (Hypertext Transfer Protocol)**
+
+Used by **web browsers and servers** to transfer web pages and data.
+
+- **Client-Server** based (browser is the client).
+    
+- Runs over **TCP** (usually port 80 or 443 for HTTPS).
+    
+- **Stateless**: Server doesn't remember past requests.
+    
+- Methods:
+    
+    - `GET`: Request a resource (e.g., a web page).
+        
+    - `POST`: Send data (e.g., form submission).
+        
+    - `PUT`, `DELETE`, etc. for RESTful APIs.
+        
+
+**Example**:
+
+```http
+GET /index.html HTTP/1.1
+Host: example.com
+```
+
+---
+
+### 2. **Electronic Mail (Email Protocols)**
+
+Email is delivered through multiple protocols:
+
+- **SMTP (Simple Mail Transfer Protocol)**
+    
+    - Sends emails from client → server or server → server.
+        
+    - Uses TCP (port 25, 587).
+        
+- **POP3 (Post Office Protocol v3)** and **IMAP (Internet Message Access Protocol)**
+    
+    - Used by clients to fetch and manage emails from servers.
+        
+    - POP3: Downloads and deletes from server.
+        
+    - IMAP: Keeps email on server, supports folders and syncing.
+        
+
+**Email flow**:
+
+1. User writes email → Client sends it using SMTP.
+    
+2. Server stores email.
+    
+3. Recipient fetches email using POP3 or IMAP.
+    
+
+---
+
+### 3. **DNS (Domain Name System)**
+
+Translates **domain names** (like `google.com`) into **IP addresses** (like `142.250.64.78`).
+
+- Works like a **phonebook** for the internet.
+    
+- Uses **UDP** (port 53).
+    
+- Hierarchical system with:
+    
+    - **Root servers**
+        
+    - **Top-level domain (TLD) servers** (.com, .org, etc.)
+        
+    - **Authoritative name servers** (e.g., Google’s DNS)
+        
+
+**Example**: Typing `www.example.com` triggers a DNS lookup: → gets IP address → browser connects to that IP using HTTP.
+
+---
+
+## 🔑 Summary
+
+|Protocol|Purpose|Transport|Port|
+|---|---|---|---|
+|HTTP|Web pages & APIs|TCP|80/443|
+|SMTP|Sending emails|TCP|25/587|
+|POP3|Receiving (download)|TCP|110|
+|IMAP|Receiving (sync)|TCP|143|
+|DNS|Resolving domain names|UDP|53|
+
+---
+
+> [!Note] These protocols are just the **tip of the iceberg** — the internet uses dozens more, but HTTP, Email, and DNS are the backbone of most everyday activity.
+
+Let me know if you want this in a PDF or if you'd like diagrams added!