Network Protocols

Network protocols are standardized rules for data communication between computers and devices.

Why Network Protocols Matter

• Standardization - Devices from different manufacturers can communicate
• Reliability - Ensure data reaches destination correctly
• Efficiency - Optimize how data is transmitted
• Security - Protect data from eavesdropping
• Scalability - Support networks of any size

OSI Model Layers

Layer 7: Application (HTTP, FTP, SMTP, DNS)
Layer 6: Presentation (SSL/TLS, encryption)
Layer 5: Session (session management)
Layer 4: Transport (TCP, UDP)
Layer 3: Network (IP)
Layer 2: Data Link (Ethernet)
Layer 1: Physical (cables, signals)

Protocol Categories

Layer 3 (Network Layer)

• IP (Internet Protocol) - Routing and addressing
  • IPv4 - 32-bit addresses
  • IPv6 - 128-bit addresses

Layer 4 (Transport Layer)

• TCP - Reliable, connection-oriented
• UDP - Fast, connectionless

Layer 7 (Application Layer)

• HTTP/HTTPS - Web communication
• DNS - Domain name resolution
• SMTP/POP3/IMAP - Email protocols
• FTP/SFTP - File transfer
• SSH - Secure shell
• Telnet - Remote access
• DHCP - IP address assignment

Key Concepts

Ports

• Numbers 0-65535
• Well-known ports (0-1023): SSH (22), HTTP (80), HTTPS (443), DNS (53)
• Registered ports (1024-49151): Applications
• Dynamic ports (49152-65535): Client connections

Sockets

• Combination of IP address + port
• Example: 192.168.1.100:8080
• Represents unique connection endpoint

Packet Structure

Header: Protocol info (source, destination, type)
Payload: Actual data
Footer: Error checking (CRC)

Common Protocols We'll Cover

1. TCP/IP - Foundation of modern internet
2. UDP - Fast, unreliable transport
3. DNS - Convert domains to IPs
4. HTTP/HTTPS - Web communication
5. SSL/TLS - Encryption and security
6. DHCP - Automatic IP assignment
7. FTP/SFTP - File transfer
8. Email Protocols - SMTP, POP3, IMAP

Learning Tips

• Understand the OSI model first
• Learn TCP/IP before application protocols
• Use tools like tcpdump and Wireshark to see protocols in action
• Understand port numbers and their meanings
• Know which protocols are encrypted (HTTPS, SSH, SFTP)
• Understand client-server model

Best Practices

• Use HTTPS instead of HTTP
• Use SSH instead of Telnet
• Use SFTP instead of FTP
• Understand protocol limitations
• Choose right protocol for use case
• Monitor protocol usage
• Keep protocols updated
• Understand security implications

Let's dive into each protocol and understand how they work.