knock

#!/bin/bash
# usage: knock HOST PORT1 PORT2 ... PORTx
# source: https://wiki.archlinux.org/index.php/Port_knocking#Port_knocking_script
# Mikrotik ROS example:
: '
;;; Knock knock #1
chain=input action=add-src-to-address-list protocol=tcp address-list=knockknock#1 address-list-timeout=15s dst-port=??? log=no log-prefix=""
;;; Knock knock #2
chain=input action=add-src-to-address-list protocol=tcp src-address-list=knockknock#1 address-list=knockknock#2 address-list-timeout=15s dst-port=??? log=no log-prefix=""
;;; Knock knock #3
chain=input action=add-src-to-address-list protocol=tcp src-address-list=knockknock#2 address-list=trusted_public_ip address-list-timeout=1m dst-port=??? log=no log-prefix=""
'
HOST=$1
shift
for ARG in "$@"
do
    nmap -Pn --host_timeout 100 --max-retries 0 -p $ARG $HOST >/dev/null
done