Overview
This lecture explains the most important network protocols and their well-known port numbers, highlighting their purposes and typical use cases for communication on modern networks.
Well-Known Port Numbers & Protocols
- Well-known port numbers are standardized so clients, servers, and firewalls can communicate consistently.
- Firewalls use port numbers to decide whether to allow network traffic.
File Transfer Protocols
- FTP (File Transfer Protocol) uses TCP port 20 for data and TCP port 21 for control, often requiring authentication.
- FTP allows file listing, upload, deletion, and renaming on the server.
Remote Terminal Access
- SSH (Secure Shell) uses TCP port 22 for encrypted command-line access to remote devices.
- Telnet uses TCP port 23 for clear-text, non-encrypted terminal access and is not recommended for production use.
Email Protocols
- SMTP (Simple Mail Transfer Protocol) uses TCP port 25 for sending email and mail server communication.
- POP3 (Post Office Protocol v3) uses TCP port 110 for receiving email, designed for single-client access.
- IMAP4 (Internet Message Access Protocol v4) uses TCP port 143 for email retrieval and mailbox synchronization across devices.
Web and Internet Access
- HTTP (Hypertext Transfer Protocol) uses TCP port 80 for non-encrypted web traffic.
- HTTPS (Hypertext Transfer Protocol Secure) uses TCP port 443 for encrypted web communication.
Network Name & Address Resolution
- DNS (Domain Name System) uses UDP port 53 to resolve domain names to IP addresses.
- DHCP (Dynamic Host Configuration Protocol) uses UDP ports 67 and 68 to assign IP addresses dynamically, with leasing and reservation options.
Windows File & Print Sharing
- SMB (Server Message Block) uses TCP port 445 for direct file and print sharing in Windows.
- NetBIOS uses UDP port 137 for naming and TCP port 139 for session and data transfer (mainly for older systems).
- CIFS (Common Internet File System) is another name for SMB.
Network Management & Directory Services
- SNMP (Simple Network Management Protocol) uses UDP port 161 for queries and UDP port 162 for trap alerts.
- SNMP v1/v2 send data unencrypted; SNMP v3 adds encryption, integrity, and authentication.
- LDAP (Lightweight Directory Access Protocol) uses TCP port 389 for directory queries such as Active Directory.
Remote Desktop Access
- RDP (Remote Desktop Protocol) uses TCP port 3389 to remotely control or access applications on Windows systems.
Key Terms & Definitions
- Port Number — Numeric identifier for a network service.
- Firewall — Device or software that controls network traffic based on rules.
- Protocol — A set of rules for communication between devices.
- Encryption — Securing data by converting it into unreadable format.
Action Items / Next Steps
- Memorize the key port numbers and their associated protocols.
- Review differences between encrypted and non-encrypted protocols.
- Practice identifying which protocol/port to use for various network tasks.