Discovering hosts with TCP SYN ping scans

Ping scans are used for detecting live hosts in networks. Nmap's default host discovery process sends TCP SYN, TCP ACK, and ICMP packets to determine whether a host is responding, but if a firewall is blocking these requests, it will be treated as offline. Fortunately, Nmap supports a scanning technique named the TCP SYN ping scan, which is very handy for probing different ports in an attempt to determine whether a host is online or at least has more permissive filtering rules.

This recipe will talk about the TCP SYN ping scan and its related options.

How to do it...

Open your terminal and enter the following command:

# nmap -sn -PS <target>

You should see a list of hosts found in the target range using TCP SYN ping scanning:

# nmap -sn -PS 192.1.1/24
Nmap scan report for 192.168.0.1 
Host is up (0.060s latency). 
Nmap scan report for 192.168.0.2 
Host is up (0.0059s latency). 
Nmap scan report for 192.168.0.3...