Computer networking devices use network  ports to communicate in the application layer. There are many well-known ports, registered ports, and dynamic/private ports to learn about, here is a list of commonly used ports and their associated uses:

• Port 21: FTP (File Transfer Protocol) – Used for transferring files between computers.
•  Port 22: SSH (Secure Shell) – Used for secure remote access and file transfers.
•  Port 23: Telnet – Used for remote terminal access (unencrypted, less secure, mostly replaced by SSH).
• Port 25: SMTP (Simple Mail Transfer Protocol) – Used for sending email.
• Port 53: DNS (Domain Name System) – Used for translating domain names to IP addresses.
• Port 67 and 68: DHCP (Dynamic Host Configuration Protocol) – Used for automatic IP address configuration.
• Port 80: HTTP (Hypertext Transfer Protocol) – Used for web browsing.
• Port 110: POP3 (Post Office Protocol 3) – Used for receiving email.
• Port 143: IMAP (Internet Message Access Protocol) – Used for accessing email on a mail server.
• Port 443: HTTPS (Hypertext Transfer Protocol Secure) – Used for secure web browsing.
• Port 587: SMTP Submission – Used for sending email from clients to servers.
• Port 3306: MySQL Database – Used for database management.
• Port 3389: RDP (Remote Desktop Protocol) – Used for remote desktop access.
• Port 5900: VNC (Virtual Network Computing) – Used for remote desktop sharing.
• Port 8080: Alternative HTTP port often used for web proxies and caching servers.
• Port 8888: Alternative HTTP port often used for web servers or proxy servers.
• Port 1433: Microsoft SQL Server Database – Used for database management.
• Port 1521: Oracle Database – Used for Oracle database connections.
• Port 161 and 162: SNMP (Simple Network Management Protocol) – Used for network management and monitoring.
• Port 389: LDAP (Lightweight Directory Access Protocol) – Used for accessing directory services.
• Port 443: HTTPS (Hypertext Transfer Protocol Secure) – Used for secure web browsing.
• Port 3306: MySQL Database – Used for database management.
• Port 5432: PostgreSQL Database – Used for database management.
• Port 636: LDAPS (LDAP over TLS/SSL) – Secure version of LDAP.
• Port 873: rsync – Used for efficient file synchronization and transfer.
• Port 995: POP3 over SSL/TLS – Secure email retrieval using POP3.
• Port 993: IMAP over SSL/TLS – Secure email retrieval using IMAP.
• Port 1433: Microsoft SQL Server Database – Used for database management.
• Port 1521: Oracle Database – Used for Oracle database connections.
• Ports 49152-65535: Dynamic/Private Ports – Used for temporary and private purposes.

Knowing the different ports used by networking devices helps with troubleshooting, setup and security of a network and its devices. It is critical to understand the function of each port to ensure the security and functionality of devices on a network. This also helps Network and System administrators when troubleshooting network issues.