What is a port lookup?
A port lookup helps identify the network service commonly associated with a TCP or UDP port number. Network applications use port numbers so that multiple services can communicate through the same IP address while remaining logically separate.
For example, TCP port 443 is commonly associated with HTTPS, port 22 with SSH and port 3389 with Remote Desktop Protocol. A port lookup is useful when reviewing firewall rules, troubleshooting services, studying networking or interpreting network documentation.
What is a network port?
A network port is a logical endpoint identified by a number from 0 to 65535. Port numbers work together with IP addresses and transport protocols such as TCP and UDP to direct network traffic to the correct application or service.
One computer can therefore run many network services at the same time. A web server might listen on TCP port 443, while an SSH service on the same machine listens on TCP port 22.
TCP vs UDP ports
TCP and UDP both use port numbers, but they are different transport protocols. TCP establishes a connection and provides ordered, reliable delivery. UDP is connectionless and typically has less overhead.
The same numeric port can theoretically be used separately for TCP and UDP. That is why a complete port reference should consider both the port number and the transport protocol.
Port number ranges
| Range | Category | Typical Use |
|---|---|---|
| 0–1023 | Well-known ports | Common and standardized network services |
| 1024–49151 | Registered ports | Applications and vendor-registered services |
| 49152–65535 | Dynamic / private ports | Temporary client ports and private application use |
Common TCP and UDP ports
| Port | Protocol | Service | Purpose |
|---|---|---|---|
| 22 | TCP | SSH | Secure remote access |
| 25 | TCP | SMTP | Email transfer |
| 53 | TCP/UDP | DNS | Domain name resolution |
| 80 | TCP | HTTP | Web traffic |
| 123 | UDP | NTP | Network time synchronization |
| 443 | TCP | HTTPS | Encrypted web traffic |
| 445 | TCP | SMB | Windows file and printer sharing |
| 587 | TCP | SMTP Submission | Authenticated email submission |
| 3389 | TCP/UDP | RDP | Remote Desktop |
How to use the port lookup
- Enter a port number, such as 443 or 3389.
- You can also enter a service name such as HTTPS, SSH, DNS or RDP.
- Click Look Up Port.
- Review the associated transport protocol, service name and typical use.
Port lookup vs port checker
A port lookup and a port checker perform different jobs. A port lookup is a reference tool that tells you what a port is commonly used for. It does not make a network connection.
A port checker attempts to determine whether a specific port on a host is reachable from the network. If you need to test whether a service is actually accessible, use the Port Checker rather than this reference lookup.
Frequently asked questions
What port is HTTPS?
HTTPS commonly uses TCP port 443 for encrypted web traffic.
What port is SSH?
SSH commonly uses TCP port 22 for secure remote command-line access and related services such as SFTP.
What port does DNS use?
DNS commonly uses both UDP and TCP port 53. UDP is widely used for normal queries, while TCP is also used for specific operations and larger responses.
What is port 3389?
Port 3389 is commonly associated with Microsoft's Remote Desktop Protocol, or RDP.
What is port 445?
TCP port 445 is commonly associated with Server Message Block, or SMB, used for Windows file and printer sharing and related services.
Does a port number always belong to one service?
No. Port numbers have common or registered uses, but applications can often be configured to listen on different ports. A lookup therefore describes typical usage rather than guaranteeing what is running on a particular host.