A port number is a 16-bit numeric value ranging between 0 and 65535, with three categories: well-known ports, registered ports, and dynamic ports. These are essential to network communication and relevant for certification study (CCNA or CompTIA Network+). Port numbers are assigned and maintained by IANA and enable application communication via TCP or UDP protocols.
How does a port work?
Computers feature two port types: physical ports (connecting peripheral devices) and network communication ports (enabling computer-to-computer network communication). Network communication ports operate at the Transport layer via TCP/UDP protocols, directing incoming traffic to appropriate protocols.
Types of communication ports
Three categories exist:
- Well-known ports: 0 through 1023
- Registered ports: 1024 through 49151
- Dynamic/private ports: 49152 through 65535
Well-Known Port Numbers Cheat Sheet
| Port | Service Name | Description |
|---|---|---|
| TCP/20, TCP/21 | File Transfer Protocol (FTP) | Sends and receives files between systems |
| TCP/22 | Secure Shell (SSH) | Encrypted console login |
| TCP/22 | Secure FTP (SFTP) | Secure File Transfer |
| TCP/23 | Telnet | Remote console login to network devices |
| TCP/25 | Simple Mail Transfer Protocol (SMTP) | Transfer emails between email servers |
| TCP/53, UDP/53 | Domain Name System (DNS) | Convert domain names into IP addresses |
| UDP/67, UDP/68 | Dynamic Host Configuration Protocol (DHCP) | Automated IP addressing and configuration |
| UDP/69 | Trivial File Transfer Protocol (TFTP) | A very simple file transfer application |
| TCP/80 | HyperText Transfer Protocol (HTTP) | Web server communication |
| TCP/110 | Post Office Protocol (POP3) | Receive mail into a mail client |
| UDP/123 | Network Time Protocol (NTP) | Synchronize clocks |
| TCP/143 | Internet Message Access Protocol (IMAP4) | A newer mail client protocol |
| UDP/161 | Simple Network Management Protocol (SNMP) | Gather statistics and manage network devices |
| TCP/389 | Lightweight Directory Access Protocol (LDAP) | Communicate with network directories |
| TCP/443 | Hypertext Transfer Protocol Secure (HTTPS) | Web server communication with encryption |
| TCP/445 | Server message block (SMB) | Windows file transfers and printer sharing |
| TCP/636 | Lightweight Directory Access Protocol Secure (LDAPS) | LDAP over SSL |
| TCP/3389 | Remote Desktop Protocol (RDP) | Graphical display of remote device |
| H.323 | ITU Telecommunication H.32x protocol series | Voice over IP signaling |
| TCP/5060-5061 | Session Initiation Protocol (SIP) | Voice over IP signaling protocol |