N etwork Scanning Basics
The second phase of ethical hacking is network scanning — this is when a hacker (or ethical hacker) checks a target network to find active devices, open ports, and running services.
In socket-based programming, the server is the one that provides a service, and the client is the one that uses it. A socket is basically an IP address + a port number. For example, an email service might use the socket 202.9.85.49:25.
In this phase, we’ll try port scanning, which means checking which ports are open on a host.
Why does this matter? Because network services can be vulnerable. Some services have weak spots like bad code, weak passwords, unencrypted data, or allowing connections from anywhere. These can all be entry points for attackers. That’s why it’s best to only keep necessary ports open to reduce the risk.
There are several ways to scan using Nmap, such as:
- Connect scan (
-sT) - TCP SYN scan (
-sS) - TCP FIN scan (
-sF) - TCP Xmas Tree scan (
-sX) - TCP Null scan (
-sN) - TCP ACK scan (
-sA) - TCP Window scan
- TCP RPC scan
You can learn more about these types of scans here.