Port Knocking
Table of content
Description
Port knocking is a security by obscurity technique that allows to open a port when some port are knocked in a defined order.
For example, the port 22 is filtered. If anyone send a SYN packet on port 567, 356 and 4000 then the port 22 will appear open.
Nmap
for x in 567 356 4000; do nmap -Pn --host_timeout 201 --max-retries 0 -p $x server_ip_address; done