What is a port scanner
A port scanner is a network diagnostic tool that allows you to determine which ports are open on a server, computer, or other device connected to the internet. Each network service operates through a specific port, so checking open ports helps to understand which services are accessible from outside.
When port scanning is performed, the tool attempts to establish a connection with the specified ports on the target IP address or domain. Depending on the server’s response, a port may have one of the following statuses:
- Open – a service is running on the port and accepts connections
- Closed – no service is running on the port
- Filtered – the connection is blocked by a firewall or network rules
Checking open ports helps to identify available services, diagnose network problems, and ensure that the server is configured correctly.
Why check open ports
Port scanning is used in various tasks of network administration, development, and information security.
Server security check
Open ports may indicate that network services are running on the server. If a service should not be accessible from the internet, it should be closed or restricted through a firewall.
Network problem diagnostics
If a service does not respond or is unavailable, a port scanner helps determine whether the required port is open or blocked at the network level.
Server configuration check
After setting up a web server, database, or another application, it is important to ensure that the required port is indeed available for connection.
Infrastructure monitoring
Developers and DevOps specialists often use port scanning to check the availability of services at different stages of infrastructure deployment.
How an online port scanner works
An online port scanner attempts to connect to the specified ports on the target IP address or domain. If the server responds to the request, the port is identified as open.
The verification process usually includes several steps:
- The user enters an IP address or domain name.
- The tool sends requests to the selected ports.
- The server’s response is analyzed.
- The results are displayed in a table with the status of each port.
Since scanning is performed from our server, the result shows how the target host looks from the public internet.
Which ports are most often checked
Some network ports are used most frequently because popular internet services operate through them.
| Port | Service |
| 80 | HTTP (web servers) |
| 443 | HTTPS (secure websites) |
| 22 | SSH remote access |
| 21 | FTP file transfer |
| 25 | SMTP mail server |
| 3306 | MySQL database |
| 3389 | Remote Desktop |
If one of these ports is open, it usually means that the corresponding service is running on the server.
When an open port is not a problem
Open ports do not always mean a security threat. Many services must be accessible from outside to function properly.
For example:
- a web server must use port 80 or 443 so that the site is accessible to users
- remote administration may use SSH (22)
- API services may run on non-standard ports
It is only important to ensure that only the ports that are truly necessary are open.
How to use a port scanner
Checking open ports with the tool is very simple:
- Enter the IP address or domain.
- Select the type of port scan.
- Click the Scan button.
- Wait for the results.
After the scan is complete, the tool will show a list of checked ports and their status.
Additional tools for network diagnostics
If you are analyzing a network connection or checking a server, other tools may also be useful:
- My IP – shows your current public IP address
- IP Lookup – allows you to find geolocation and network information of an IP address
- Proxy Checker – checks the functionality of proxy servers
Using these tools together helps to quickly identify the cause of network problems and get a complete picture of the connection.
FAQ
Frequently asked questions
Here we answered the most frequently asked questions.
Is port scanning legal?
Scanning your own servers or systems for which you have permission is a common administrative practice. However, checking other networks without permission may violate terms of use or the law.
Why might a port appear as filtered?
This means that a firewall or security system is blocking the connection attempt, so it is impossible to determine exactly whether the port is open or closed.
Can a firewall hide open ports?
Yes. Modern security systems can filter requests and prevent scanners from determining the real status of a port.