🔥 Networking Basics & Anonymity (Proxy, VPN, Tor) Explained for Hackers 🔥

📌 1. OSI Model & TCP/IP Model

📜 OSI Model (7 Layers)

1. Physical Layer – Bits, cables, wireless signals.
2. Data Link Layer – MAC addresses, ARP, switches.
3. Network Layer – IP addresses, routing.
4. Transport Layer – TCP/UDP, port numbers.
5. Session Layer – Session establishment (e.g., SSL/TLS).
6. Presentation Layer – Encryption, data formats (JPEG, MP3, etc.).
7. Application Layer – HTTP, FTP, DNS, etc.

🌐 TCP/IP Model (4 Layers)

1. Network Interface – Physical + Data Link layer.
2. Internet Layer – IP addresses, routing.
3. Transport Layer – TCP/UDP, port numbers.
4. Application Layer – HTTP, FTP, DNS, etc.

📌 Important Notes:

• OSI is theoretical; TCP/IP is practical.
• TCP/IP combines layers (e.g., No "Presentation" or "Session" layer).

---

📌 2. IP Addressing (IPv4/IPv6, Subnetting, CIDR)

📌 IPv4 (32-bit, 4 octets)

• Example: 192.168.1.1
• Private IP Ranges:
  • 10.0.0.0 – 10.255.255.255
  • 172.16.0.0 – 172.31.255.255
  • 192.168.0.0 – 192.168.255.255

📌 IPv6 (128-bit, 8 blocks)

• Example: 2001:0db8:85a3:0000:0000:8a2e:0370:7334
• Uses hexadecimal.
• No subnetting needed like IPv4.

📌 Subnetting & CIDR

• Subnet Mask: Divides network & host.
  • 255.255.255.0 → /24 (CIDR notation)
  • 255.255.0.0 → /16
• CIDR (Classless Inter-Domain Routing): Efficient IP allocation.
  • /24 = 256 IPs (1 network, 254 usable).
  • /30 = 4 IPs (2 usable).
  • /32 = 1 IP (single host).

📌 Commands to Check IP:

bash

ip a   # Linux
ifconfig   # Older Linux/macOS
ipconfig   # Windows

---

📌 3. MAC Addresses & ARP

MAC Address (Media Access Control)

• Unique identifier (48-bit) for network interfaces.
• Example: 00:1A:2B:3C:4D:5E
• Can't be routed like IP addresses.

ARP (Address Resolution Protocol)

• Maps IP to MAC in LAN.
• Command to check ARP table:

  bash
  
  arp -a   # Windows/Linux/macOS
  

🔥 Hacking Use-Case: ARP Spoofing (Man-in-the-Middle Attack)

bash

arpspoof -i eth0 -t TARGET_IP -r GATEWAY_IP

---

📌 4. Ports & Protocols (TCP, UDP, ICMP, etc.)

🔗 Common Protocols

Protocol	Port	Usage
TCP	-	Reliable, connection-oriented
UDP	-	Fast, connectionless
ICMP	-	Ping, network diagnostics
HTTP	80	Web traffic
HTTPS	443	Secure web traffic
FTP	21	File transfer
DNS	53	Domain name resolution
SMTP	25	Sending email
SSH	22	Secure shell (remote access)

📌 Checking Open Ports

bash

netstat -tulnp   # Linux
netstat -ano   # Windows

Or using Nmap:

bash

nmap -p- TARGET_IP

---

📌 5. DNS Resolution (nslookup, dig, host)

DNS (Domain Name System) converts domain names into IPs.

📌 Commands for DNS Lookup

bash

nslookup google.com    # Windows/Linux/macOS
dig google.com         # Linux/macOS
host google.com        # Linux/macOS

📌 Check all DNS Records:

bash

dig google.com ANY

---

🔥 Proxy, VPN, and Tor Basics (Anonymity Techniques) 🔥

📌 1. Proxy Servers

A proxy acts as an intermediary between you and the internet.

Types of Proxies:

1. Forward Proxy – For users accessing the internet.
2. Reverse Proxy – For servers to protect web apps.
3. SOCKS Proxy – Handles multiple protocols (SOCKS5 supports UDP).
4. Transparent Proxy – Invisible to the user.

📌 Using a Proxy (Linux)

bash

export http_proxy="http://proxy_ip:port"
export https_proxy="https://proxy_ip:port"

For Nmap Scan via Proxy:

bash

nmap --proxy http://proxy_ip:port -p80 example.com

---

📌 2. VPN (Virtual Private Network)

A VPN encrypts your internet traffic and routes it through a secure server.

📌 Benefits: ✅ Hides IP address.
✅ Bypasses geo-restrictions.
✅ Encrypts traffic.

📌 VPN Services:

• NordVPN
• ExpressVPN
• ProtonVPN (Free)
• OpenVPN (Self-hosted)

📌 Check VPN Connection:

bash

curl ifconfig.me   # Check your public IP

---

📌 3. Tor (The Onion Router)

Tor encrypts your traffic through multiple relays, making tracking difficult.

📌 Install Tor on Linux:

bash

sudo apt update && sudo apt install tor -y

📌 Start Tor Service:

bash

tor

📌 Use Tor with Curl:

bash

torsocks curl ifconfig.me

📌 Anonymize Browsing (TOR Browser)

• Download from https://www.torproject.org/
• Routes traffic through multiple nodes.

---

🔥 Conclusion & Hacking Use Cases 🔥

🚀 Mastering networking helps in:
✅ Bug Bounty (Understanding network vulnerabilities).
✅ Penetration Testing (Exploiting network misconfigurations).
✅ Anonymity (Using VPN, Proxy, and Tor for privacy).

🛠 Next Steps

1️⃣ Practice with Wireshark for packet analysis.
2️⃣ Learn MITM attacks (Ettercap, Bettercap).
3️⃣ Explore dark web using Tor safely.