The most important network ports to know
Nicolas,
When two machines communicate on a network, they do not only exchange data via an IP address — they do so through ports, numerical entry points that allow different types of traffic to be distinguished. Knowing the most common network ports is essential for understanding how the internet works, securing a server or diagnosing a connection problem.
What is a network port?
A network port is a number associated with a connection between two machines. Combined with the IP address, it forms what is called a socket — the complete address of a service on the network. If the IP address identifies the machine, the port identifies the service or application that must handle the communication.
Ports are numbered from 0 to 65,535 and fall into three categories:
- Well-known ports (0–1023): reserved for standard system services (HTTP, FTP, SSH…)
- Registered ports (1024–49151): used by known third-party applications
- Dynamic ports (49152–65535): temporarily assigned by the system for outgoing connections
The most important network ports
| Port | Protocol | Service | Description |
|---|---|---|---|
| 20 / 21 | TCP | FTP | File transfer (data / control) |
| 22 | TCP | SSH | Secure remote connection |
| 23 | TCP | Telnet | Unencrypted remote connection (obsolete) |
| 25 | TCP | SMTP | Sending emails between servers |
| 53 | TCP/UDP | DNS | Domain name resolution to IP addresses |
| 80 | TCP | HTTP | Unencrypted web browsing |
| 110 | TCP | POP3 | Email reception (local download) |
| 143 | TCP | IMAP | Email reception (server synchronisation) |
| 443 | TCP | HTTPS | Encrypted web browsing (SSL/TLS) |
| 3306 | TCP | MySQL | MySQL/MariaDB database |
| 3389 | TCP | RDP | Windows remote desktop |
| 5432 | TCP | PostgreSQL | PostgreSQL database |
| 8080 | TCP | Alternative HTTP | Alternative web server or HTTP proxy |
Port 80 and port 443: HTTP vs HTTPS
Port 80 is used by the HTTP protocol for standard web browsing, without encryption. Port 443 is its secure equivalent: it carries HTTPS traffic, encrypted via SSL/TLS. Today, almost all websites automatically redirect HTTP traffic (port 80) to HTTPS (port 443).
Good to know: when you type a URL into your browser without specifying a port, your browser automatically uses port 80 for HTTP and port 443 for HTTPS. These ports are called implicit because they do not appear in the URL.
Port 22: SSH, the cornerstone of server administration
SSH (Secure Shell) on port 22 is the standard protocol for securely connecting to a remote server. All communications are encrypted, making it the direct successor to Telnet (port 23), now abandoned because it transmitted data in plain text.
Port 22 is one of the first targets of automated scans on the internet. It is recommended to:
- Change the default SSH port on your servers
- Disable password authentication in favour of SSH keys
- Use a firewall to restrict the IP addresses allowed to connect
Port 53: DNS, the internet directory
DNS (Domain Name System) on port 53 is the service that translates domain names into IP addresses. When you type example.com in your browser, a DNS query is sent on port 53 to a DNS resolver to obtain the corresponding IP address.
DNS generally uses UDP for fast queries, and TCP for large responses or zone transfers between DNS servers.
Open ports and network security
Every open port on a server or router represents a potential attack surface. An open port running a vulnerable or misconfigured service can be exploited by an attacker.
- Regularly scan your open ports with tools like nmap to verify that only necessary services are exposed
- Close unnecessary ports — port 23 (Telnet) and port 21 (FTP) should never be open on a public server
- Use a firewall to filter incoming connections by port and source IP address
Good to know: your public IP address is the identifier that other machines use to contact you on the internet. Combined with a port number, it forms the complete address of a service accessible from outside. You can check your public IP address and analyse the associated information directly from our online tool.