Firewalls

A firewall is a network security system that controls the incoming and outgoing network traffic based on an applied rule set. A firewall establishes a barrier between a trusted, secure internal network and another network (e.g., the Internet) that is assumed not to be secure and trusted. Firewalls exist both as a software solution and as a hardware appliance. Many hardware-based firewalls also offer other functionality to the internal network they protect, such as acting as a DHCP server for that network.

Many personal computer operating systems include software-based firewalls to protect against threats from the public Internet. Many routers that pass data between networks contain firewall components and, conversely, many firewalls can perform basic routing functions.

Firewall_Image

Generation of Firewalls
  • First generation: packet filters
  • Second generation: "stateful" filters
  • Third generation: application layer
Types
  • Network layer or packet filters
  • Application-layer
  • Proxies
  • Network address translation