Port Detection

Tool Introduction

The Port Detection tool is a convenient and efficient online network port scanning service. It allows users to enter a target IP address or domain name and specify the port number or port range to be detected, helping you quickly understand the open status of the target host's ports. Whether for network troubleshooting, verifying server service operation, or conducting preliminary network security assessments, this tool provides instant, accurate detection results, effectively improving your network diagnostic efficiency.

How to Use

1. In the "Target Address" input box, fill in the IP address or domain name you want to detect, for example: www.example.com or 8.8.8.8.
2. In the "Port Number/Range" input box, enter the port number(s) you wish to detect. You can enter a single port (e.g., 80), multiple ports (separated by commas, e.g., 21,22,80,443), or a port range (e.g., 1-1024), or a combination thereof.
3. Click the "Start Detection" button, and the tool will immediately probe the port status of the specified target.
4. Wait a moment, and the detection results will be displayed in the area below, clearly showing the open status of each port.

Input Parameter Format

• Target Address: Supports IPv4 addresses (e.g., 192.168.1.1) or valid domain names (e.g., www.baidu.com).
• Port Number/Range:
  • Single port: 80
  • Multiple ports: 21,22,80,443
  • Port range: 1-1024
  • Combined use: 20,21,80-90,443
  Port numbers must be integers between 1 and 65535.

Output Result Format

The tool will return the status of each detected port in a list, including:

• Open: Indicates that a service is listening on this port and successfully responded to the connection request.
• Closed: Indicates that no service is listening on this port, but the target host itself is reachable.
• Filtered: Indicates that a firewall or other network device blocked the probe to this port, making it impossible to determine its true status.
• The response time for each port may also be displayed.

Usage Example

Below is a practical example of using the port detection tool:

• Example Input Data:
  • Target Address: www.baidu.com
  • Port Number/Range: 80,443,22
• Specific Operation Demonstration:
  1. Open this port detection tool page.
  2. Fill in www.baidu.com in the "Target Address" input box.
  3. Fill in 80,443,22 in the "Port Number/Range" input box.
  4. Click the "Start Detection" button.
• Expected Output Results (may vary slightly depending on actual conditions):

  Port Number	Status	Notes
  80	Open	Web service (HTTP) running normally
  443	Open	Encrypted Web service (HTTPS) running normally
  22	Closed or Filtered	SSH service not open or blocked by firewall

Frequently Asked Questions

• Q: What is the principle of the port detection tool? A: The port detection tool sends probe requests (usually TCP SYN requests) to specific ports on the target IP address or domain name, and then determines the port's status based on the target host's response. If a SYN-ACK response is received, the port is open; if an RST response is received, the port is closed; if no response is received or an ICMP error is received, it may be filtered by a firewall.
• Q: Why do some ports show a "Filtered" status? A: When port detection results show "Filtered", it usually means that a firewall, intrusion detection/prevention system (IDS/IPS), or other network security device has intercepted our probe request, preventing direct access to that port. In this case, the tool cannot definitively determine whether the port is open or closed, only that a security policy is obstructing it.
• Q: What are the specific meanings of "Open" and "Closed" ports? A:
  • Open: Indicates that the target host is running a service on that port, and the service is listening and ready to accept connections. For example, port 80 being open usually means a web server is running.
  • Closed: Indicates that the target host is reachable, but no service is listening on that port. Although the port is closed, we can confirm that the host itself is active.
• Q: Can I detect UDP ports? A: This tool primarily focuses on TCP port detection. The detection mechanism for UDP ports is different from TCP, more complex, and results are more uncertain. For UDP port detection, please use professional command-line tools.

Uses and Significance of Port Detection

Port detection plays a crucial role in network management and security, with wide-ranging uses and significance:

• Network Troubleshooting: When a remote service is inaccessible, checking whether the corresponding port on the target server is open is a common troubleshooting step. For example, if a website cannot be opened, you can detect ports 80 or 443; if SSH cannot connect, detect port 22.
• Server Service Verification: System administrators can use port detection to confirm whether specific services on a server have successfully started and are listening. This helps quickly diagnose issues with service startup failures or configuration errors.
• Network Security Auditing: Port scanning is an important part of security auditing. By scanning, unexpected open ports can be discovered, which may represent potential security vulnerabilities or misconfigurations that need to be closed or strengthened promptly.
• Penetration Testing Information Gathering: In legitimate penetration testing activities, port scanning is the first step in gathering information about the target system. Open ports can reveal the types and versions of services the target system might be running, providing a basis for subsequent attack surface analysis.
• Firewall Rule Verification: Administrators can use port detection to verify whether firewall rules are working as expected, for example, confirming whether a certain port has been correctly allowed or blocked.

In summary, port detection is not only an essential tool for daily network maintenance but also an important means of building and maintaining a secure network environment.

Notes

• Compliant Use: Please ensure that you use this tool for port detection only with authorization. Unauthorized scanning of others' networks may involve legal risks and could be considered malicious behavior.
• Network Environment Impact: The accuracy of detection results may be affected by your own network environment, the target server's network configuration (such as firewalls, IDS/IPS), and network latency. For example, a firewall may set a port to "Filtered" status, rather than truly open or closed.
• Reasonable Frequency: Please avoid performing a large number or high frequency of port scans on the same target within a short period, as this may be identified as an attack by the target server and trigger defense mechanisms, leading to IP blocking or distorted detection results.
• Port Range Limits: To ensure service quality and prevent abuse, this tool may set limits on the number or range of ports for a single detection.