portscan（From Target to Access Understanding Port Scanning）

From Target to Access: Understanding Port Scanning

Port scanning is a vital tool for network reconnaissance. It is the process of probing a network or a host to identify the open ports and the services running on them. Port scanning is often the first step that attackers take while planning their attacks, but it can also be used by legitimate administrators to identify vulnerabilities in their networks. In this article, we will discuss the basics of port scanning and how it can be used for better network security.

What is Port Scanning?

In TCP/IP networking, a 'port' is a communication endpoint. Each port number corresponds to a specific service, such as HTTP on port 80 or SSH on port 22. When a client wishes to communicate with a server, it must connect to the server's IP address and the specific port number used by the service it wishes to access.

Port scanning is the process of scanning a range of IP addresses and testing each IP address against a list of common open ports by sending packets to each one. Port scanning tools can be used by attackers to identify vulnerable hosts, services, and unsecured network connections.

Types of Port Scans

There are different types of port scans, each with its purpose and advantages. The three most common types of port scans are:

1) SYN Scan

The SYN scan is the most common type of port scan. It works by sending a SYN packet to the target host and waiting for a response. If the port is open, the target will respond with a SYN/ACK packet. If the port is closed, the target will respond with a RST (reset) packet. If the port is filtered, there will be no response at all. SYN scanning is an effective way of detecting open ports quickly.

2) Stealth Scan

The Stealth scan aims to avoid detection by the target by initiating low-level traffic. It does not complete a three-way handshake and sends a packet without setting the SYN flag. The result is that if the target is using a stateful firewall, it will not register the scan. The Stealth scan is harder to detect, but it is also slow since it does not complete the handshake process.

3) XMAS Scan

The XMAS scan employs a different approach by using packets with all flags set (PSH, FIN, URG). Since these packets do not map to the common communication patterns, most firewalls will drop them. If the target is configured to drop packets rather than to reject them, it can be used to identify open ports with no response, indicating an open port.

Why Port Scanning is Important for Network Security?

Port scanning has legitimate uses in network security, such as testing the security of the system or assessing the risks associated with giving network access to a new device. Port scanning is useful in the following ways:

1) Assessing Vulnerabilities

By using a port scanner, network administrators can test their systems for open ports and services. Scanning the network identifies ports that are in use and any services that may pose potential security risks. Once vulnerabilities are detected, they can then be addressed to improve the overall security posture of the network.

2) Preventing Unauthorized Access

Port scanning can be used as an offensive measure to identify open ports and services on the network. By conducting regular scans, administrators can detect and remove unauthorized services or unauthorized devices on the network, hardening the network's overall security.

3) Threat Detection

Port scanning can also be used as part of network intrusion detection. By monitoring traffic, administrators can detect scans and other attacks and take appropriate action to mitigate them.

Conclusion

In summary, port scanning can be an essential part of network administration and security. Port scanning can identify the open ports and services, determine the vulnerabilities, and harden the overall security posture of the network. However, like many tools, port scanning can be used maliciously. Therefore, understanding how port scanning works, the different types of port scans, and how to prevent them is crucial for securing your network.