Port Knocking

Knock

knock 192.168.1.2 1000:tcp 2000:tcp 3000:tcp            # normal                                                           
knock 192.168.1.2 1000:tcp 2000:tcp 3000:tcp -v         # verbose
knock 192.168.1.2 1000:tcp 2000:tcp 3000:tcp -v -d 50   # delay

for x in 1000 2000 3000; do nmap -Pn --max-retries 0 -p $x 192.168.1.2; done
for x in 1000 2000 3000; do nmap -Pn --host_timeout 201 --max-retries 0 -p $x 192.168.1.2; done

hping3 -S 192.168.1.2 -p 1000 -c 1 ; hping3 -S 192.168.1.2 -p 2000 -c 1 ; hping3 -S 192.168.1.2 -p 3000 -c 1

Files

/etc/knockd.conf