Link Kumpulan M.Port Knocking1. http://translate.google.co.id/translate?hl=id&sl=en&u=https://www.digitalocean.com/community/tutorials/how-to-use-port-knocking-to-hide-your-ssh-daemon-from-attackers-on-ubuntu&prev=search2. https://translate.google.com/translate?depth=1&hl=id&prev=search&rurl=translate.google.co.id&sl=en&u=https://www.digitalocean.com/community/tutorials/how-to-use-fwknop-to-enable-single-packet-authentication-on-ubuntu-12-043. https://translate.googleusercontent.com/translate_c?depth=2&hl=id&prev=search&rurl=translate.google.com&sl=en&u=https://www.digitalocean.com/community/tutorials/how-to-configure-port-knocking-using-only-iptables-on-an-ubuntu-vps&usg=ALkJrhjVXdRzZRi0N3KYT_DHoIsbAz9vtw4. http://translate.google.co.id/translate?hl=id&sl=en&u=http://www.cipherdyne.org/fwknop/&prev=search5. http://en.wikipedia.org/wiki/Port_knocking#Benefits6. http://www.linuxjournal.com/article/68117. http://www.linuxjournal.com/article/3546