The TCP ACK scanning technique uses packets with the flag ACK on to try to determine if a port is filtered. This technique comes handy when checking if the firewall protecting a host is stateful or stateless.
This recipe shows how to perform TCP ACK port scanning by using Nmap.
Open your terminal and type the following command:
#nmap -sA <target>
The output follows the standard port format:
# nmap -sA 192.168.1.254 Nmap scan report for 192.168.1.254 Host is up (0.024s latency). All 1000 scanned ports on 192.168.1.254 are unfiltered MAC Address: 5C:4C:A9:F2:DC:7C (Huawei Device Co.)
The argument -sA tells Nmap to launch a TCP ACK port scan against the target host. The TCP ACK port scanning technique works in the following way:
A packet with the flag ACK is sent to each selected port.
If the port is open or closed, a RST packet is sent by the target machine. This response also indicates that the target host...