There are several tools available online to check for open ports on a computer or device. Here are some of the most commonly used tools:

• Port Checker: This is a simple and free online tool for checking open ports on your computer/device. It is often useful in testing port forwarding settings on a router. Port numbers range from 1 to 65535, out of which well-known ports are pre-defined as convention by IANA. The most commonly used ports include HTTP, SMTP, DHCP, FTP, etc.

• YouGetSignal Open Port Check Tool: This tool is useful for finding out if your port forwarding is set up correctly or if your server applications are being blocked by a firewall. It may also be used as a port scanner to scan your network for ports that are commonly forwarded. Some of the most important ports include FTP, SSH, TELNET, SMTP, DNS, HTTP, POP3, SSL, SMB, MSSQL, MySQL, Remote Desktop, PCAnywhere, VNC, and Minecraft.

• DNS Checker Open Port Scanner: This tool checks if a specific port is open and accessible on a target system. It combines traditional TCP and UDP scanning techniques to ensure 100% accurate results. This helps you understand your networks connectivity status and flag potential vulnerabilities. You can ask the tool which types of ports to check, such as ports used for gaming, applications, or sharing files.

• IONOS Port Check: This tool tells you which methods are available for checking open ports. It explains that open ports are not only communication points between your systems and the Internet or other computers, but also points of attack from malware and hackers. Regularly checking for open ports ensures that only the ports you actually need are open. The most important ports are standardized ports with the numbers 0 to 1023 for fixed applications. Ports 1024 to 49151 are assigned both for fixed applications and dynamically, while ports 49152 to 65535 are assigned dynamically.

• NetStat.exe: This is a built-in tool in Windows 10 that shows protocol statistics and the current TCP and IP network connections. The two commands needed to identify open ports are netstat -ab and netstat -aon. The former lists all active ports and the processs name that uses them, while the latter identifies open ports.

• Canyouseeme.org Open Port Check Tool: This is a free utility for remotely verifying if a port is open or closed. It is useful to users who wish to verify port forwarding and check to see if a server is running or a firewall or ISP is blocking certain ports. The most commonly blocked ports are port 80 and port 25. Port 80 is the default port for http traffic, while port 25 is the default port for sending and receiving mail. ISPs block these ports to reduce the amount of spam generated by worms on infected machines within their network.

It is important to note that open ports can be a security risk if they are not properly secured. Hackers might exploit open ports to gain unauthorized access to a network or device. Monitoring and securing open ports to maintain network security regularly is important.