A useful reference guide for IT professionals, students, and anyone troubleshooting network connectivity issues.
Introduction
Network ports allow devices and applications to communicate across a network. Different services use specific port numbers to send and receive data.
When troubleshooting connectivity issues, reviewing firewall rules, or configuring applications, understanding common port numbers can be extremely useful.
What Is a Network Port?
A network port is a logical communication endpoint used by network services.
For example:
IP Address + Port Number = Network Connection
192.168.0.100:80
This indicates a device listening for web traffic on port 80.
TCP vs UDP
| Protocol | Description |
|---|---|
| TCP | Connection-oriented, reliable communication |
| UDP | Faster but connectionless communication |
Some services use both TCP and UDP.
Common Networking Ports
| Port | Protocol | Service | Description |
|---|---|---|---|
| 20 | TCP | FTP Data | File transfer data channel |
| 21 | TCP | FTP Control | File Transfer Protocol |
| 22 | TCP | SSH | Secure remote administration |
| 23 | TCP | Telnet | Legacy remote terminal access |
| 25 | TCP | SMTP | Email message delivery |
| 53 | TCP/UDP | DNS | Domain Name Resolution |
| 67 | UDP | DHCP Server | Assigns IP addresses to devices |
| 68 | UDP | DHCP Client | Receives IP address assignments |
| 69 | UDP | TFTP | Simple file transfer service |
| 80 | TCP | HTTP | Standard website traffic |
| 88 | TCP/UDP | Kerberos | Active Directory authentication |
| 110 | TCP | POP3 | Email retrieval |
| 123 | UDP | NTP | Network time synchronisation |
| 135 | TCP | RPC | Windows Remote Procedure Calls |
| 137 | UDP | NetBIOS Name Service | Windows network name resolution |
| 138 | UDP | NetBIOS Datagram | Windows browsing services |
| 139 | TCP | NetBIOS Session | Legacy file sharing |
| 143 | TCP | IMAP | Email retrieval protocol |
| 161 | UDP | SNMP | Network device monitoring |
| 162 | UDP | SNMP Trap | Network alerts and monitoring |
| 389 | TCP/UDP | LDAP | Active Directory directory services |
| 443 | TCP | HTTPS | Secure website traffic |
| 445 | TCP | SMB | Windows file and printer sharing |
| 465 | TCP | SMTPS | Secure email transport |
| 514 | UDP | Syslog | Logging and event collection |
| 587 | TCP | SMTP Submission | Secure email sending |
| 636 | TCP | LDAPS | Secure LDAP communications |
| 993 | TCP | IMAPS | Secure IMAP email access |
| 995 | TCP | POP3S | Secure POP3 email access |
| 1433 | TCP | Microsoft SQL Server | Database communications |
| 1521 | TCP | Oracle Database | Database communications |
| 3306 | TCP | MySQL | Database services |
| 3389 | TCP | RDP | Windows Remote Desktop |
| 5432 | TCP | PostgreSQL | Database communications |
| 5900 | TCP | VNC | Remote desktop access |
| 8080 | TCP | Alternate HTTP | Web services and proxies |
Microsoft and Active Directory Ports
| Port | Protocol | Service |
|---|---|---|
| 53 | TCP/UDP | DNS |
| 88 | TCP/UDP | Kerberos |
| 123 | UDP | NTP |
| 135 | TCP | RPC Endpoint Mapper |
| 389 | TCP/UDP | LDAP |
| 445 | TCP | SMB |
| 636 | TCP | LDAPS |
| 3268 | TCP | Global Catalog |
| 3269 | TCP | Secure Global Catalog |
| 3389 | TCP | Remote Desktop |
These ports are commonly encountered in Microsoft 365, Active Directory, and domain environments.
Ports Often Used in Home Networks
| Port | Service | Common Purpose |
|---|---|---|
| 53 | DNS | Website name lookups |
| 67/68 | DHCP | Automatic IP addressing |
| 80 | HTTP | Web browsing |
| 443 | HTTPS | Secure web browsing |
| 3389 | RDP | Remote Desktop |
| 445 | SMB | File and printer sharing |
Common Troubleshooting Examples
Website Not Loading
Check: Port 80 (HTTP) and/or Port 443 (HTTPS)
Possible causes:
- Firewall blocking traffic
- Internet connectivity issue
- Website unavailable
Testing Ports Using PowerShell
Example:
Test-NetConnection www.rbosworth.com -Port 443
Output:
Quick Reference: Most Common Ports
| Port | Service |
|---|---|
| 22 | SSH |
| 25 | SMTP |
| 53 | DNS |
| 80 | HTTP |
| 88 | Kerberos |
| 110 | POP3 |
| 123 | NTP |
| 143 | IMAP |
| 389 | LDAP |
| 443 | HTTPS |
| 445 | SMB |
| 587 | SMTP Submission |
| 636 | LDAPS |
| 993 | IMAPS |
| 995 | POP3S |
| 1433 | SQL Server |
| 3306 | MySQL |
| 3389 | Remote Desktop |
Key Takeaway
Many common networking and application issues can be traced back to blocked, unavailable, or incorrectly configured ports. Understanding the most commonly used port numbers can significantly speed up troubleshooting and help identify where communication is failing between devices, applications, and services.