Lecture on Network Protocols and Port Numbers

Importance of Port Numbers

• Port numbers are crucial for devices to communicate over networks.
• Known as well-known port numbers because both server and client need to know them.
• Firewalls use port numbers to allow or disallow traffic.
• Memorizing port numbers may seem tedious but becomes easier with use.
• Knowing which protocols use which port numbers is essential.

FTP - File Transfer Protocol

• Used for transferring files between devices.
• Ports:
  • TCP port 20: Used for data transfers.
  • TCP port 21: Used to control data transfer.
• Requires authentication (username and password or anonymous access).
• Includes file management functions (list, add, delete, rename files).

SSH - Secure Shell

• Provides terminal connection to remote devices.
• Port: TCP port 22.
• Offers encrypted communication (secure).

Telnet

• Provides text-based front-end connection to remote devices.
• Port: TCP port 23.
• Sends communication in the clear (non-encrypted).
• Not recommended for production networks (use SSH instead).

SMTP - Simple Mail Transfer Protocol

• Used by email servers to communicate.
• Port: TCP port 25.
• Used by clients to send mail; receiving mail uses different protocols (IMAP, POP3).

DNS - Domain Name System

• Resolves domain names to IP addresses.
• Port: UDP port 53.
• Critical for browsing as IP addresses change without notification.

DHCP - Dynamic Host Configuration Protocol

• Automatically assigns IP addresses to devices on a network.
• Ports: UDP port 67 and UDP port 68.
• Uses a leasing system for IP address assignment.
• DHCP reservations can assign the same IP to specific devices consistently.

HTTP and HTTPS

• Protocols for web browser communication with servers.
• HTTP Port: TCP port 80 (non-encrypted).
• HTTPS Port: TCP port 443 (encrypted).

POP3 and IMAP

• Protocols for receiving emails.
• POP3:
  • Port: TCP port 110.
  • Not ideal for multiple clients.
• IMAP:
  • Port: TCP port 143.
  • Suitable for synchronization across devices.

SMB - Server Message Block

• Transfers files and information between Windows systems.
• Ports:
  • UDP port 137 (name service).
  • TCP port 139 (session setup).
  • TCP port 445 (direct SMB communication).

SNMP - Simple Network Management Protocol

• Used for querying and managing network devices.
• Ports:
  • UDP port 161 (queries).
  • UDP port 162 (traps/alerts).
• Versions:
  • SNMP v1: Non-encrypted.
  • SNMP v2: Bulk transfers, non-encrypted.
  • SNMP v3: Encrypted with message integrity and authentication.

LDAP - Lightweight Directory Access Protocol

• Queries directories like Microsoft Active Directory.
• Port: TCP port 389.

RDP - Remote Desktop Protocol

• Provides remote access to Windows desktops.
• Port: TCP port 3389.
• Available in many Windows editions and compatible with various OS clients.