Mini guide on networks

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1. What is a Network?

A network is a collection of devices connected to each other to share resources (like files or the internet) and allow communication between them. Networks can be small (local networks) or large (like the internet).

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2. Types of Networks

• LAN (Local Area Network): Covers a small area (home, office), typically using Ethernet cables or Wi-Fi.
• WAN (Wide Area Network): Connects LANs over large distances (e.g., the internet).
• MAN (Metropolitan Area Network): Covers a city or metropolitan area (e.g., ISP networks).
• PAN (Personal Area Network): Connects devices over a short range, like phones and laptops (e.g., via Bluetooth).
• WLAN (Wireless Local Area Network): A wireless LAN, typically using Wi-Fi technology.

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3. Network Components

• Router: Directs traffic between different networks (e.g., between a LAN and a WAN like the internet).
• Switch: Connects multiple devices within a LAN, ensuring data is sent only to the correct recipient.
• Access Point: Extends wireless connectivity within a LAN.
• NIC (Network Interface Card): Allows a device to connect to a network.
• Firewall: Security system that filters network traffic, allowing or blocking packets based on defined rules.

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4. Network Topologies

• Star Topology: All devices are connected to a central node (switch or hub).
• Bus Topology: All devices share a single communication channel.
• Ring Topology: Devices are connected in a closed loop; data travels in one direction.
• Mesh Topology: Each device is connected to several others, providing redundancy and high reliability.

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5. Important Protocols

• TCP/IP (Transmission Control Protocol/Internet Protocol): The foundation of the internet. TCP ensures reliable data delivery, while IP handles addressing and routing.
• HTTP/HTTPS (HyperText Transfer Protocol): Used to access web pages. HTTPS is the secure version (uses SSL/TLS).
• FTP (File Transfer Protocol): Used to transfer files between devices over a network.
• DNS (Domain Name System): Converts domain names (e.g., google.com) into IP addresses.
• DHCP (Dynamic Host Configuration Protocol): Automatically assigns IP addresses to devices in a network.
• SMTP/IMAP/POP3: Protocols for sending and receiving email.

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6. IP Addresses

• Public IP: A unique address identifying a device on the internet.
• Private IP: Used within a local network, not visible on the internet.
• IPv4 vs IPv6: IPv4 uses 32-bit addresses (e.g., 192.168.1.1), while IPv6 uses 128-bit addresses, allowing many more unique addresses.
• NAT (Network Address Translation): Allows multiple devices in a local network to share a single public IP address.

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7. OSI Model (Open Systems Interconnection)

The OSI model breaks network communication into 7 layers, which help standardize and explain how networks operate:

1. Physical Layer: Electrical, optical signals, hardware (cables, switches).
2. Data Link Layer: Transmission of data over a physical link (e.g., Ethernet, MAC).
3. Network Layer: Handles routing and addressing (e.g., IP).
4. Transport Layer: Ensures reliable data delivery (e.g., TCP).
5. Session Layer: Establishes and manages sessions between applications.
6. Presentation Layer: Translates data formats and handles encryption.
7. Application Layer: Interfaces for applications (e.g., HTTP, FTP, SMTP).

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8. Network Security

• Encryption: Process of encoding data so only the intended recipient can read it.
• VPN (Virtual Private Network): Creates a secure, encrypted connection over a public network (like the internet).
• SSL/TLS: Protocols for encrypting data in transit, commonly used in HTTPS.
• WPA/WPA2/WPA3: Security protocols for Wi-Fi networks.

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9. Additional Concepts

• Bandwidth: Maximum data transfer capacity over a connection in a given time (measured in Mbps or Gbps).
• Latency: Time taken for data to travel from source to destination (measured in milliseconds).
• QoS (Quality of Service): Prioritizes certain types of traffic to ensure good performance (e.g., for video calls or gaming).
• Ping: Tool to measure latency or response time between two devices.
• VLAN (Virtual LAN): Virtual network created over physical infrastructure to segment traffic.

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10. Common Performance Metrics

• Data Transfer Rate: The amount of data that can be transmitted over a network in a given time. Measured in Mbps or Gbps.
• Jitter: Variation in packet arrival times. High jitter can affect real-time services like voice or video.
• Packet Loss: When data does not reach its destination, often due to network issues or congestion.

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Let’s imagine you're sitting at home with your laptop, and you want to visit www.google.com.

1. Private IP (within your home network):

   • Your laptop has a private IP address like 192.168.1.10 assigned by your home router using DHCP.
   • All devices connected to your router, such as your phone, tablet, or smart TV, will also have private IPs, typically in the same range (192.168.x.x), unique within your home.

2. Public IP (visible to the outside world):

   • Your router has a public IP address (e.g., 203.0.113.5) assigned by your Internet Service Provider (ISP). This is the address visible to websites and services outside your home network.
   • When your laptop sends a request to Google, the router uses NAT (Network Address Translation) to replace your laptop's private IP (192.168.1.10) with your home’s public IP (203.0.113.5).

3. DNS and IP conversion:

   • When you type www.google.com in your browser, your router uses DNS (Domain Name System) to convert that domain name into Google's IP address. For example, it might resolve to 172.217.16.206 (Google’s IP).

4. Communication:

   • Your request is sent from your public IP address (203.0.113.5) to Google’s public IP (172.217.16.206).
   • Google receives the request, processes it, and sends back the data (the website content) to your public IP address.

5. NAT and Private IP Return:

   • When the response from Google reaches your router, NAT translates the public IP (203.0.113.5) back to your laptop's private IP (192.168.1.10), and your laptop receives the data.

So:

• Private IP: Used within your local network (192.168.1.10 for the laptop).
• Public IP: Used to communicate with the internet (203.0.113.5 for your home network).
• DNS: Converts a domain name (www.google.com) to an IP address (172.217.16.206).