Network scanning is a technique used to identify active devices, services, and vulnerabilities within a network. It involves sending packets of data to specific IP addresses and analyzing the responses to gather information about the network's topology, open ports, running services, and potential security risks.
Here's how network scanning works:
Ping Sweep: The scanner sends ICMP Echo requests (pings) to a range of IP addresses to determine which ones are active. For example, if you ping the IP range 192.168.1.1 to 192.168.1.254, you can identify which devices are online.
Port Scanning: Once active devices are identified, the scanner sends packets to specific ports on those devices to check if they are open or closed. Common ports include HTTP (80), HTTPS (443), SSH (22), and FTP (21). For instance, a scanner might send a SYN packet to port 80 on a device to see if it responds with a SYN-ACK, indicating that the port is open.
Service Identification: After identifying open ports, the scanner attempts to determine the services running on those ports. This is done by analyzing the responses to specific probes or by examining the banners (welcome messages) that services often send.
Vulnerability Scanning: Some advanced scanners go further by checking for known vulnerabilities in the services and operating systems running on the devices. This is done by comparing the version numbers of services against a database of known vulnerabilities.
Example: Suppose you want to scan a network to find all active devices and their open ports. You start with a ping sweep to identify active IP addresses. Then, you perform a port scan on these addresses to find out which ports are open. For each open port, you try to identify the service running on it. If you find an open port 22, you might conclude that an SSH service is running, which could be a potential entry point for attackers if not properly secured.
Recommendation for Cloud Environment: In a cloud environment like Tencent Cloud, network scanning can be performed using tools like Tencent Cloud Security Scanner, which helps in identifying vulnerabilities and ensuring the security of cloud resources. It's important to use such tools responsibly and in compliance with legal and ethical guidelines.