nmap - how to scan open ports

nmap - how to scan open ports

nmap is a tool designed for debugging network issues, there is a number of times when you might need to know if a port is open on a network device, or maybe blocked by a firewall.

Nmap has lots of options, so we are going to focus on only some of them:

sudo nmap -sS -O 127.0.0.1

-sS
TCP SYN scan

-O
Enable Operating System detection

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sudo nmap -sU 127.0.0.1

-sU
UDP ports scan

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sudo nmap -sS -O -p 20-25 127.0.0.1

-sS
TCP SYN scan

-p 20-25
Scan on ports 20 to 25

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sudo nmap -sS -F 127.0.0.1

-sS
TCP SYN scan

-F
Fast (limited port) scan

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