Port Scanners

Port scanners are essential tools in the troubleshooting and cybersecurity landscape. They are designed to detect open or closed network ports on a target system. Network ports serve as communication endpoints for various applications and services running on a device, and knowing the status of these ports can help identify potential security vulnerabilities or confirm that specific services are running as intended.

In this section, we will explore the following aspects of port scanners:

• Why port scanners are important
• Types of port scanners
• Popular port scanning tools

Why port scanners are important

Port scanners can help in the following situations:

• Identifying open ports: Open ports might expose your system to attacks if they are left unsecured. A port scanner can help you identify which network ports are open and need to be secured.
• Detecting unauthorized services: Scanning for open ports can help you find if any unauthorized applications are running on your network, as these services might open ports that you are not aware of.
• Testing firewall rules: Port scanners can also verify if your firewall rules are effective and configured correctly.
• Troubleshooting network issues: By detecting open and closed ports, port scanners can help you diagnose network problems and ensure your applications and services are running smoothly.

Types of port scanners

There are three main types of port scanners:

• TCP Connect: This scanner initiates a full TCP connection between the scanner and the target device. It goes through the entire process of establishing a TCP connection, including a three-way handshake. This type of scan is accurate but more easily detectable.
• TCP SYN or Half-Open scan: This scanner only sends a SYN packet (a request to start a connection) to the target device. If the target device responds with a SYN/ACK packet, the port is considered open. This type of scan is faster and less detectable, as it doesn’t establish a full connection.
• UDP Scan: This scanner targets User Datagram Protocol (UDP) ports, which are typically used for streaming and real-time communication applications. It sends UDP packets to the target device, and if there’s no response, the port is considered open. This type of scan can be less accurate, as some devices may not respond to UDP probes.

Popular port scanning tools

Here are some popular and widely used port scanning tools:

• Nmap: Nmap (Network Mapper) is a free, open-source tool that is highly versatile and powerful. It offers various types of scans, including TCP Connect, TCP SYN, and UDP scans.
• Masscan: Masscan is a high-speed port scanner that is typically used for large-scale scanning, thanks to its ability to scan the entire internet within a few minutes.
• Angry IP Scanner: It is a cross-platform port scanner that is very user-friendly and suitable for beginners. It supports both TCP and UDP scanning.

Remember to always use port scanners responsibly and only on your own systems or where you have permission to perform a scan. Unauthorized port scanning can have legal and ethical implications.