Firewall Components

Contents

• Section Overview

• Filtering Routers

  • How packets are filtered out?

  • What information is used for filtering decision?

  • Examples

    • Protecting from the IP spoofing of internal addresses

    • Allowing only electronic mail traffic

  • Why Filtering Routers are not enough?

  • Further Study

• Application Gateways - Proxies

  • Overview

  • How proxy program works?

  • How  external client is enforced to contact proxy server?

  • How  internal client is enforced to contact proxy server?

  • Further Study

Section Overview

As was mentioned above firewall must inspect all the packets that come to and leave the Local Network and filter out those packets that do not conform to the Security Policy  adopted for the Local Network.

Remember the ISO seven layers protocol model. The packet inspection can take place on any of the layers. But packet inspection is most commonly implemented at Application layer by Application layer firewalls and at Network layer by Network layer firewalls.

When talking about TCP/IP protocol suite the Application layer firewalls are commonly called Application Gateways or Proxies(further Proxies) and Network layer firewalls Filtering Routers or Screening Routers(further Filtering Routers).