Fire wall

What is a Firewall?

A firewall is a system that protects a computer or a computer network against intrusions coming from a third-party network (generally the Internet). A firewall is a system that filters data packets that are exchanged over the network.

 

• an interface for the network being protected (internal network)
• an interface for the external network
  

The firewall system is a software system, often supported by dedicated network hardware, forming an intermediary between the local network(or the local computer) and one or more external networks. A firewall system can be set up on any computer that uses any system as long as:

• The machine is powerful enough to process the traffic
• The system is secure
• No other service other than the packet filtering service is running on the server

In the case that a firewall system is provided in a black box, the term "appliance" applies.

How a Firewall System Works

 

 A firewall system contains a set of predefined rules that allow the system to: 

 

• Authorise the connection (allow)
• Block the connection (deny)
• Reject the connection request without informing the issuer (drop)

All of these rules implement a filtering method that depends on the security policy that was adopted by the organisation. Security policies are usually broken down into two types that allow:

• the authorisation of only those communications that were explicitly authorised:
  
  
  
  
  
  
  
  

  "Everything that is not explicitly authorised is prohibited"

  
  
  
  
  
  
  
  
  
  
  
• the refusal of exchanges that were explicitly prohibited

The first method is without a doubt the safest. However, it imposes a precise and restrictive definition of communication needs.