Web Penetration Testing with Kali Linux - Third Edition

Different options for port scan

The straightforward way of running an Nmap port scan is called the TCP connect scan. This option is used to scan for open TCP ports, and it is invoked using the -sT option. The connect scan performs a full three-way TCP handshake (SYN-SYN / ACK-ACK). It provides a more accurate state of the port, but it is more likely to be logged at the target machine and slower than the alternative SYN scan. A SYN scan, using the -sS option, does not complete the handshake with the target, and it is therefore not logged on that target machine. However, the packets generated by the SYN scan can alert firewalls and IPS devices, and they are sometimes blocked by default by such appliances.

Nmap, when invoked with the -F flag, ...