Port Knocking Port knocking is one of hardening method to prevent unauthorized user access the services. This method ability to externally open ports that, by default, keep closed by firewall. It works by sending TCP packets to predefined closed ports in right order. In my virtual environment, I have two Linux based systems one is Debian8 and the other is Centos7. Debian8(Server): IP: 192.168.17.139 Services: knockd,ssh Centos7(client): IP: 192.168.17.135 Services: ssh

Q: Is is possible to get free SSL certificate, which is supported by modern web browsers such as Chrome, Mozilla Firefox, IE etc,. A: Actually, yes you can have free green bar SSL certificates which is supported by modern web browsers. Let’s Encrypt is a free, automated, open Certificate Authority. But before you have SSL certificate, It requires some of the things you have to do to confirm you are the owner of domain that you want to get SSL certificate.