Understanding Ports in Networking

Introduction to Ports

• Definition: A port is a logical connection used by programs and services for exchanging information.
  • Not a physical connection.
  • Determines the specific program/service to be used on a computer/server.
• Usage Examples:
  • Web pages, FTP services, accessing email.
• Unique Identification:
  • Ports are identified by numbers ranging from 0 - 65535.
  • Common Ports:
    • Port 80 and 443: Web pages.
    • Port 21: FTP.
    • Port 25: Email.

Ports and IP Addresses

• IP Address: A numeric address serving as an identifier for a device on a network.
• Communication: An IP address and a port number work together to exchange data on a network.
  • IP address locates the server.
  • Port number determines the service/program to use.

Example Use Case

• Port 80 (HTTP):
  • Used when visiting web pages.
  • Example: Accessing google.com:
    • Domain name resolves to Google's IP address.
    • Port 80 is appended for HTTP service.

Netstat Utility

• Purpose: Displays current network connections and port activity.
• Usage:
  • Command: netstat -n (shows actual port numbers).
  • Output: Local address, IP address, port numbers, foreign address (e.g., google.com).

FTP Example

• Port 21:
  • Standard protocol for file transfer between computers and servers.
  • Example: Accessing ftp.google.com:
    • Domain name resolves to IP address.
    • Port 21 is appended for FTP service.

Port Number Ranges

• Categories:
  • 0 - 1023: System/well-known ports (e.g., 80, 443, 25, 21).
  • 1024 - 49151: User/registered ports (can be registered by companies).
  • 49152 - 65535: Dynamic/private ports (client-side ports, assigned temporarily).

Server vs. Client Port Usage

• Well-known and Registered Ports:
  • Used on servers.
• Dynamic/Private Ports:
  • Used on clients (temporary assignment during a session).
• Client Acting as Server:
  • Computers can act as servers, using well-known ports (e.g., 21 or 80).

Example Command Output

• Connecting to Websites: Example with yahoo.com and example.com, using ports like 80.
• FTP Connection: Using port 21.

Port 443 and HTTPS

• Port 443:
  • Used for secure web pages (HTTPS).
  • Port 80 vs. Port 443:
    • Port 80: Unsecured (HTTP).
    • Port 443: Secured (HTTPS).

Additional Resources

• Networking Knowledge: Book recommendations and Audible trial for learning.
• Further Learning: Video on netstat utility available on the presenter's channel.

Note: Subscribe to the presenter's channel for more networking videos.