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Firewall Security

A Firewall is a dedicated network box (usually implemented in the organisation's "gateway" router) situated between the Internet and an organisation's private network, thus:
Simple firewall structure
There are three classes of Firewall:
  1. Packet filtering firewalls
  2. Application gateways
  3. Circuit level gateways

 
Of these, the packet filtering type is the most common.
 
Because the firewall is not a general-purpose host, it does not itself run any vulnerable server processes.
 


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