A firewall is a system that can control both incoming and outgoing data based on rules that are either user or manufacturer set, or a combination of both. A firewall can either be hardware-based or software-based. Microsoft Windows includes a software-based firewall. All versions of CentOS after CentOS 7 include a Dynamic Firewall Manager [ fireewalld] . Common manufacturers of hardware-based firewall systems include Cisco and Juniper.
