TCP/IP Fundamentals

TCP/IP Protocol Suite

The TCP/IP model is the foundation of modern networking, defining how data is transmitted across networks.

The Four Layers

Application Layer

• HTTP, HTTPS, FTP, SSH, DNS, SMTP
• User-facing protocols
• Data formatting and presentation

Transport Layer

• TCP - Reliable, connection-oriented
• UDP - Fast, connectionless
• Port numbers and segmentation

Internet Layer

• IP - Addressing and routing
• ICMP - Error reporting and diagnostics
• Packet fragmentation

Network Access Layer

• Ethernet, Wi-Fi
• MAC addressing
• Physical transmission

TCP vs UDP

TCP Three-Way Handshake

Client              Server
  |                   |
  |------- SYN ------>|
  |                   |
  |<--- SYN + ACK ----|
  |                   |
  |------- ACK ------>|
  |                   |
  |   Connection      |
  |   Established     |

IP Addressing

IPv4 Structure

• 32-bit address
• Dotted decimal notation (192.168.1.1)
• Network and host portions

IPv6 Structure

• 128-bit address
• Hexadecimal notation (2001:db8::1)
• Built-in security features

Common Ports

Port    Protocol    Service
20-21   TCP         FTP
22      TCP         SSH
23      TCP         Telnet
25      TCP         SMTP
53      TCP/UDP     DNS
80      TCP         HTTP
443     TCP         HTTPS
3306    TCP         MySQL
5432    TCP         PostgreSQL
6379    TCP         Redis

Packet Flow Example

# Trace packet path
traceroute google.com

# Capture packets
tcpdump -i eth0 -n port 80

# Analyze with tshark
tshark -i eth0 -f "tcp port 443"

Best Practices

1. Understand layers - Know which protocol operates where
2. Use TCP for reliability - When data integrity matters
3. Use UDP for speed - Real-time applications
4. Monitor traffic - Regular packet analysis
5. Secure ports - Close unnecessary services